Peptide serum: ingredients, claims and scientific evidence

A peptide serum is a cosmetic product containing one or more peptide ingredients. It can take the form of an aqueous solution, a gel, a lightweight gel serum or an emulsion. It usually also contains other ingredients that affect hydration, texture, stability, product spreadability and skin feel.

The term „serum” itself does not denote a specific concentration of peptides, their depth of penetration, biological mechanism, or level of efficacy.

Research into peptide serums includes controlled human studies, open-label studies, before-and-after product analyses, laboratory experiments, ex vivo skin studies, and chemical analyses. Each of these types of study answers different scientific questions, and therefore they should not be treated as equivalent.

A human clinical trial may show changes after using a ready-made serum, but it does not necessarily confirm that the peptides were responsible for all the observed effects. Nor does it prove that every peptide in the formula contributed equally, that a higher number of peptides yields a better result, that the ingredient reached a specific living layer of the skin, or that the serum is more effective than a cream containing similar ingredients.

Therefore, it is worth starting the assessment of evidence regarding the peptide serum with the entire formulation rather than just the word „peptide”.

The most important questions are:

• Which peptides are in the product?
• Are these chemically defined molecules?
• What other ingredients does the formulation contain?
• Is the peptide concentration known?
• Does the given percentage refer to the pure peptide or the entire mixture of ingredients?
• Was the actual finished product tested?
• Has an appropriate comparison group been used?
• What parameters were measured?
• Has percutaneous penetration been demonstrated if the proposed mechanism requires it?

Terms like „multi-peptide”, „10-peptide complex”, „skin booster”, „advanced delivery system” or „clinically tested” only become scientifically useful when they can be linked to specific information regarding composition, formulation and research.

What is a peptide serum?

The serum is a ready-to-use cosmetic formulation

A serum combines various ingredients into a finished product designed for application to the skin's surface. Many serums have a relatively light consistency, yet the category itself encompasses various physical systems.

Some formulations are primarily aqueous. Others may contain oils, emulsifiers, silicones, polymers, humectants, lipid structures or dispersed phases.

The appearance and consistency of the serum therefore say relatively little about the peptide content or the biological activity of the product. A transparent appearance does not indicate the amount of peptide, and a watery consistency does not mean a high concentration. Similarly, a light formula is not proof of deep penetration through the skin.

Peptides are molecules built from amino acids. Their sequences and chemical modifications can affect, among other things, interactions with other substances, stability, solubility and behaviour in a cosmetic formulation. More basic information about this group of molecules can be found in the explanatory guide what peptides are, how they work and how they are classified.

For example, palmitoylated peptides have a group derived from a fatty acid attached, whereas acetylated peptides have a different chemical modification. Such information helps to characterise the ingredient, but the name alone does not yet determine the effect of the finished cosmetic product on human skin.

The serum also contains a base, which is the formulation surrounding the active ingredients. It should not be treated as an insignificant background, as the base itself can influence the product's effect.

Humectants, emollients, solvents, film-forming agents and other formulation ingredients can influence hydration, smoothness, elasticity, skin feel, surface appearance and light reflection — independently of the proposed mechanism of action of the peptide. The science of moisturisers considers both the direct action of these ingredients and the role of the vehicle in delivering other substances. [1]

This means that the peptide serum can cause several overlapping effects. The improvement in skin feel may stem primarily from the moisturising system, and the temporary smoothing from hydration or the action of film-forming substances. Changes in the appearance of fine lines may be the result of the interaction of several ingredients, whereas the proposed cellular response may require a completely different type of experimental evidence.

Calling all these results simply „peptide action” blurs important scientific distinctions.

A peptide serum does not mean a single type of peptide

The serum may contain a single defined peptide sequence, several different peptides, chemically modified peptides, peptide-metal complexes, hydrolysates containing peptide fragments, patented mixtures, or more complex compositions that also contain amino acids, proteins, extracts, and other substances.

These are chemically different materials.

For example, a protein hydrolysate may contain many different fragments instead of a single precisely defined sequence. A formulation containing free amino acids and proteins is also not chemically equivalent to a product consisting solely of defined short peptides.

One study evaluated a serum containing a patented „peptide-pro complex”, which is a blend of neuropeptides, proteins, amino acids and marine extracts. The study included ex vivo experiments and a 12-week human part, in which the results were compared with the participants' baseline state. [2]

The results therefore relate to this specific mixture, this formulation and these experimental conditions. They do not allow a single peptide to be isolated as the cause of the observed changes. Nor do they imply that neuropeptides, proteins, amino acids and peptide fragments are the same material.

A practical rule of thumb when analysing research on peptide serums is simple: first, one must determine what the tested material actually contained. A similar claim on the front of the packaging is not enough to consider two formulations scientifically equivalent.

A broader discussion of the various types of peptides used in cosmetics, their formulation, and the limitations of the evidence can be found in the article Peptides in skin care: action, formulation and scientific evidence.

„Booster primarily describes product positioning

A peptide skin booster is typically a serum or similar product, presented as an additional step in the skincare routine.

However, the word „booster” on its own does not mean that the product increases the penetration of other cosmetics, enhances the efficacy of another active ingredient, works synergistically with a moisturising cream, or makes the entire routine clinically more effective. Each of these claims can be tested experimentally.

To demonstrate that a booster improves the efficacy of an existing routine, it would be best to compare the same routine used on its own with the identical routine supplemented by the booster. If several products are introduced simultaneously, the study is already answering a different question.

Similarly, a study in which participants add a serum to their existing skincare routine may provide information on such real-world usage, but it does not prove that adding another step brings benefits to every routine.

An open-label study of a face and neck serum containing 10 peptides involved 48 subjects over 12 weeks. Participants were divided according to their previous skincare routines, and the researchers described an improvement in selected parameters of skin quality. [3]

However, this was not a randomised comparison of 10 peptides with six, one or no peptides. Both groups received the serum, so the study does not confirm that the number of peptides alone was responsible for the observed improvement.

How to read the ingredients of a peptide serum?

Start with the full name of the ingredient

The full name of the ingredient provides more information than the generic term „peptide”. It may indicate the length of the molecule, acetylation, palmitoylation, metal complexation or other modifications.

However, numbers appearing in the names of cosmetic peptides can easily be misinterpreted.

For example, „hexapeptide” means a peptide composed of six amino acid residues. The additional identification number appearing in the name of a cosmetic ingredient is usually used to distinguish a specific ingredient and does not necessarily indicate the number of peptides found in the product.

Meanwhile, the marketing term „six-peptide blend” usually refers to the stated number of peptide ingredients. These numbers therefore describe completely different characteristics.

Scientific terminology and cosmetic nomenclature can also differ. When comparing a product with research, it is worth checking the chemical identity, sequence — if known — modification, formulation and terminology used by the researchers, rather than assuming that similarly sounding names mean identical substances.

The order of the ingredients does not reveal the exact concentration of the peptide

The INCI list provides useful information about the composition, but it is not a complete quantitative description of the formula.

For example, the US FDA sets out a general principle that cosmetic ingredients should be listed in descending order of concentration, whilst providing for exceptions relating, amongst other things, to ingredients present at a concentration of 1% or lower, and colourants. [4] Other jurisdictions have their own rules, which must be assessed separately.

A peptide located at the end of the ingredient list is therefore not automatically ineffective. At the same time, the fact that one peptide is positioned higher than another does not allow their exact quantitative ratio to be determined.

The actual concentration, chemical stability, purity, behaviour in formulation, skin exposure, and concentration at the site of the proposed biological action may still remain unknown.

Research into some peptides has been carried out at relatively low concentrations. However, this does not mean that the appropriate question is: „Do peptides work at low concentrations?”. A more precise question is: „Has this specific peptide, at this concentration and in this formulation, been investigated for a specific effect?”.

In a well-known palmitoyl pentapeptide study, a moisturiser containing this peptide was compared with a corresponding peptide-free cream, and differences in skin appearance parameters were noted. [5] The result supports the tested formulation, but does not establish a universal concentration suitable for every peptide serum.

The percentage of the mixture does not have to mean the percentage of the pure peptide

Percentage claims require particularly careful interpretation.

Let’s imagine a label bearing the words „10% peptide complex”. This does not necessarily mean that 10% of the finished product consists of pure peptide molecules.

Every percentage requires specification of what exactly is in the numerator and denominator. The given amount may refer to the pure peptide, raw material solution, proprietary blend or preparation containing the peptide along with water, solvent and other ingredients.

These are not equivalent values.

Hypothetically, a manufacturer might use 10% in the finished serum, supplied by the manufacturer as a solution. If the raw material itself contains only part of the active peptide, the finished product will not contain 10% as a pure peptide.

This is a general rule concerning ingredients and does not mean that a specific manufacturer has mislabelled the product.

If the basis of the percentage value is not explained, the actual pure peptide content may remain unknown.

Analytical chemistry allows this issue to be assessed more directly. In studies utilising liquid chromatography coupled with tandem mass spectrometry, palmitoyl peptides were quantified in cosmetic matrices. [6]

Such an analysis can confirm the chemical content, but an important distinction still applies:

chemical content ≠ skin penetration ≠ biological activity ≠ clinical efficacy.

Each of these questions requires separate evidence.

Pay attention to the ingredients next to the peptides

Peptide serums often contain many non-peptide ingredients. These may include glycerin, hyaluronic acid, niacinamide, ceramides, plant extracts, exfoliating agents, antioxidants, oils, silicones, polymers, preservatives and texture-modifying substances, among others.

Some of them may affect the same parameters that are highlighted in peptide marketing.

For instance, the improvement in hydration may result from the presence of glycerin, hyaluronic acid, other humectants, the base, peptides, or the action of several of these elements simultaneously.

The presence of multiple active ingredients does not mean that the study is invalid. It does, however, change the scope of the conclusions that can be drawn from it.

A randomised pilot study evaluated a serum containing niacinamide, postbiotics and peptides in 25 participants over four weeks. [7] Among the parameters evaluated, a difference in hydration was observed after four weeks.

Because the product contained several potentially active ingredients, the study supports the conclusions regarding the finished serum. However, it does not allow one to state that the peptides alone were independently responsible for the moisturising effect.

The ingredients list is therefore an important starting point, but it does not replace the quantitative characterisation, stability data, penetration studies or a properly controlled test of the finished product.

Formulation and declared effects

The substrate affects the availability and action of the ingredients

For the peptide to participate in the proposed activity, it must first maintain adequate stability and availability in the formulation.

Solubility, pH, oxidation, interactions with other ingredients, water content, packaging, exposure to light, storage method, and the distribution of the peptide in the formulation may all be significant.

A peptide dissolved directly in a simple laboratory solution is not automatically equivalent to the same nominal ingredient found in a complex cosmetic product.

Stability cannot be determined solely on the basis of the product's appearance either. A serum may remain transparent, homogeneous, have a normal colour and show no visible changes, even though one of the ingredients is undergoing chemical changes.

An analytical study on acetyl hexapeptide-8 analysed both the peptide itself and its oxidised form in cosmetics, as well as issues related to sample preparation. [8]

This does not mean that every peptide serum undergoes significant degradation or that every oxidized form of the peptide is harmful. The conclusion is much narrower: the ingredient name on the label does not fully describe its chemical state throughout the entire period of cosmetic use.

The light consistency of the serum does not mean deep delivery

One of the common assumptions regarding serum is the belief that its lightweight texture allows the ingredients to penetrate deeper into the skin.

However, consistency and penetration are not the same property.

A runny serum can spread easily, disappear quickly from the skin's surface, leave less of a noticeable layer or feel lighter than a cream. None of these observations prove that the intact peptide has migrated into the living layers of the skin.

The stratum corneum constitutes a significant barrier. Peptide permeation may depend on the size and charge of the molecule, hydrophilicity, lipid affinity, chemical modifications, stability, and the overall formulation.

The review of acetyl hexapeptide-8 discusses permeability limitations and uncertainty regarding access to biological sites associated with the proposed action on neurotransmission. [9] The light texture of the product does not solve this problem.

Similarly, encapsulation is a formulation strategy and not proof of site of delivery. A review of liposomal GHK-Cu highlights the limitations of available evidence regarding permeation and the need to use appropriate analytical methods. [10]

Therefore, „liposomal” does not automatically mean „reaches the dermis”.

A well-designed penetration study should distinguish whether the substance was detected on the skin surface, in the stratum corneum, viable epidermis, dermis, or the receptor fluid of the experimental diffusion system. These are distinct outcomes.

A validated LC-MS/MS method developed for the quantification of hexapeptides in matrices related to skin research demonstrates one way of analytically investigating such questions. [11] However, the mere development of a method capable of detecting the peptide does not prove that a specific serum reaches the appropriate layer of the skin.

Detection of the peptide does not imply biologically significant exposure

Even if the peptide is detected in a specific layer of the skin, another question remains: was there a sufficient amount of the intact molecule present to produce the proposed biological effect?

Modern analytical methods can detect very small amounts of substances. Therefore, mere detection does not imply biologically sufficient exposure.

In the case of the strong mechanist thesis, the chain of evidence might look as follows:

the peptide is in the formulation → remains intact → reaches the appropriate layer → achieves sufficient exposure → impacts the proposed target → a significant effect appears in humans.

Not every cosmetic claim requires confirmation of all these stages. A controlled human trial can, for example, demonstrate a visible improvement even if the exact mechanism remains uncertain.

However, if the marketing points to a specific, deep-seated biological mechanism, the delivery issue becomes particularly important.

Hydration, smoothing and the effect on collagen are different outcomes

A peptide serum can be evaluated in terms of hydration, wrinkle appearance, roughness, elasticity-related parameters, firmness, standardised photography or participant satisfaction.

Each of these results answers a different question.

Higher skin hydration does not prove collagen synthesis. Similarly, a smoother appearance of the skin does not automatically confirm dermal remodelling.

The study on GHK-Cu with hyaluronic acid described findings regarding collagen IV in fibroblasts and ex vivo skin. [12] This is useful mechanistic data, but it does not prove that every serum containing GHK-Cu and hyaluronic acid delivers an equivalent amount of ingredients, reaches the same tissues, elicits the same collagen response, or improves the appearance of wrinkles in humans.

Claims regarding expression lines require their own evidence

Some peptide serums are promoted in the context of their effect on facial expression signalling.

Such a claim requires more than just a photograph showing a smoother skin appearance.

If the proposed mechanism involves a specific neuronal or neuromuscular site, it should be established whether the peptide remains intact, whether the topical formulation delivers it to the appropriate location, whether sufficient exposure is achieved, whether the proposed biological effect occurs under realistic conditions, and whether it translates into the declared result in humans.

A review of acetyl hexapeptide-8 highlights unresolved issues regarding topical delivery and mechanism of action. [9]

Terms like „Botox-like”, „peptide-tox” or „needle-free Botox” should not, therefore, be treated as proof that a cosmetic serum is equivalent to botulinum toxin administered by injection.

A ready-made cosmetic product can improve the appearance of expression wrinkles without confirming the mechanism suggested by such terms.

How are ready-made serum tests evaluated?

First, establish what question was actually being investigated

Finished product testing relates to a specific formulation used under specific conditions. Its significance depends, amongst other things, on the characteristics of the participants, the duration, the comparison group, the previous skincare routine, the method of application, the endpoints, and the statistical analysis.

Before interpreting the result, it is worth establishing whether the serum was tested on its own, serum compared with a base, serum compared with another active product, serum added to an existing routine, or serum as one of the elements of an entirely new skincare regimen.

Each of these projects answers a different question.

Comparing the same formulation base with and without the peptide can help determine the peptide's contribution. Testing two completely different commercial products may show a difference between the finished formulations, but it will not necessarily allow you to determine which ingredient caused it.

A before-and-after product study, however, can document changes occurring during use, but it does not fully separate the product's effect from natural variability, participant expectations, measurement error, concurrent skincare routines, seasonal changes and other factors.

A study of the serum containing 10 peptides clearly shows this difference. [3] The open-label design and the groups formed on the basis of previous skincare routines allow for discussion of the changes observed during the use of the product, but they do not confirm the efficacy of the exact ten peptides or the additional effect of the serum compared to an identical routine without it.

Separate the laboratory part from human trials

One publication can cover several different types of experiments, for example cellular studies, ex vivo skin studies, chemical analyses and human product evaluation.

The probative value of one of these elements should not be automatically transferred to the others.

A good example is the study of the peptide-pro complex. [2] In the ex vivo part, comparisons were made with an untreated control and another serum, whereas the human part involved comparing participants with their own condition before starting product use.

These are two distinct research projects. The controlled laboratory comparison does not turn the human participant portion into a randomised head-to-head clinical trial.

Similarly, a 2026 publication analysed a serum containing two peptides, gluconolactone, niacinamide and Laminaria extract in ex vivo studies and two clinical trials. [13] The abstract described groups of 50 and 42 individuals, but did not confirm a randomised comparison of the finished product with an appropriate vehicle.

The results should therefore be treated as data concerning the entire formulation. The existence of a control group not described by the authors should not be assumed.

Check the comparator group and other ingredients

A suitable comparison group often provides more information than an impressive percentage improvement.

If a multi-ingredient serum improves the appearance of wrinkles compared to baseline, this result alone does not make it possible to determine whether the change was due to the peptide, the moisturizing ingredients, the retinoid, niacinamide, another active substance, the entire combination, or factors unrelated to the product.

An eight-week study of a serum containing retinaldehyde, peptides, ceramides and lipids involved 32 women. Results regarding skin appearance and tolerance were reported. [14]

Because the product contained a retinoid, peptides, ceramides, lipids, and the remaining formulation components, the results apply to the finished product. They do not independently confirm that the peptides caused the improvement or that they increased the tolerance of retinaldehyde.

To answer such questions, different comparisons would be needed.

Even a study with an active comparator requires careful interpretation. A 56-day experiment compared 0.002% of cyclised hexapeptide-9, 0.002% of retinol and a control. [15]

The results relate to specific formulations and concentrations. Identical percentage values do not imply equivalent biological activity, and a single formulation containing 0.002% of retinol is not representative of all retinol-containing cosmetics.

The statement „this peptide formulation performed better than this retinol formulation under these conditions” is therefore much more precise than the general „peptides are better than retinol”.

Sample size, observation time and uncertainty should be assessed together

Small studies can provide valuable information, but they have limitations. A smaller number of participants can mean less precise estimates, a narrower population representation and a reduced ability to detect rare adverse events. Conclusions regarding subgroups are then particularly uncertain.

The duration of the study is also important. An experiment lasting eight or twelve weeks can provide information concerning precisely that period, but without further observation it does not confirm lasting results, effects that persist for many months after discontinuation, long-term safety, or the consequences of multi-year use.

Statistical significance should be analysed alongside effect size, confidence intervals – if they have been presented – measurement variability, the response of the comparison group, the severity of changes at baseline, and the practical significance of the result.

Statistically detectable differences can be small. Conversely, participant satisfaction may depend not only on visible changes, but also on texture, fragrance, ease of spread, moisturising effect, packaging, or skin feel.

A good study should also clearly state how many participants started and completed the experiment, how missing data were handled, whether photographs were taken under standardised conditions, whether assessors were blinded where possible, and which outcomes were specified before the analysis began.

What do selected serum tests actually show?

The sources for the individual lines are [7], [3], [2], [14] and [13] respectively.

These studies show various types of evidence regarding peptide serums. They do not rank all products or provide a complete review of all studies on peptides in skincare.

Routine care products, multi-peptides and various product formats

Claims regarding routine require comparison of entire routines

Questions about how to use a peptide „skin booster” often assume that every peptide serum has a single, scientifically validated place in the skincare routine.

The studies presented do not confirm such a universal rule.

The application conditions used in the study determine what the scientists tested. The manufacturer's instructions, however, specify how to use a specific product. None of these elements automatically determines the best regimen for all peptide serums.

To determine whether adding serum improves the existing routine, it would be valuable to compare the same routine without serum with serum, while maintaining similar other conditions.

If participants introduce several new products at the same time, the study assesses the entire combination.

In a 14-week open-label study, peptidal serum was evaluated in combination with supportive skin care routine in 29 women. [16] Improvements in skin appearance parameters were noted.

Since the intervention involved several elements, it is not possible to attribute the observed changes solely to the serum, peptides, or any other element of the routine.

In another 12-week study, serum with hyaluronic acid was evaluated in combination with a cream rich in peptides. 17 people completed the study. [17]

Because both products were used simultaneously, the study does not prove that the serum was better than the cream, that the cream was better than the serum, or that the combination of both products was more effective than either product used separately.

„Multi-peptide” describes the composition, not the proven synergy

A multi-peptide serum contains more than one peptide component. However, this term does not indicate which peptides are exactly used, how many of them are present in the product, in what proportions they are present, or their stability, permeability, or mechanism of action.

Two products labeled as „10-peptide serum” can therefore have completely different compositions. One may contain ten defined synthetic peptides, while the other may contain components found in proprietary blends. Their concentrations and bases can also vary significantly.

An even stronger claim is „synergy”. It means that the combination of ingredients produces an effect greater than the one expected based on the action of the individual components when compared with each other.

Just observing an improvement after using the mixture does not confirm a synergy.

To study it, for example, one can compare peptide A, peptide B, the combination A + B, and the substrate itself. Such a project provides much more information about interactions than a study of a ready-made mixture alone.

The study of the serum containing 10 peptides did not compare equivalent products containing one peptide, several peptides, ten peptides, and no peptide at all.[3] Therefore, it does not allow for the creation of an effectiveness ranking based on the number of peptides.

Serum, cream and booster do not form a hierarchy of effectiveness

Serums and creams often differ in their formulation structure. Many creams are in the form of a semi-solid emulsion, whereas many serums are lighter liquids or gels.

Such differences can affect distribution, occlusion, evaporation, residue on the skin surface, moisturizing effects, and sensations during use. However, they do not form a universal ranking of peptide concentrations, penetration, strength of action, or effectiveness.

A reliable comparison of serum with a cream would require well-defined formulations and a study designed specifically to compare them.

If a cream and serum contain different peptides, concentrations, humectants, active ingredients, and bases, the observed difference cannot simply be attributed to the „serum versus cream” format.

The study, in which hyaluronic acid serum was used together with a cream rich in peptides, does not provide such a comparison, because both products were part of the same routine. [17]

The same principle applies to ampoules, essences, concentrates, boosters, and masks. These are terms for formulation formats or commercial positioning, not for the measure of efficacy.

Tolerance depends on the entire formulation

The serum peptide tolerance depends on the entire composition, concentration, frequency and duration of exposure, the application site, and the characteristics of the individuals using the product.

The serum may also contain other ingredients that can cause irritation or hypersensitivity. Therefore, good tolerance of a product containing peptides does not automatically mean that all peptides as a category are non-irritating. On the other hand, irritation after using a peptide serum does not automatically mean that the peptide is responsible for it.

Frameworks for the evaluation of the safety of cosmetic peptides have been proposed that also include computational methods to support safety analysis.[18] Such tools can be helpful in studies, but they do not replace experimental data, product evaluation, or relevant information regarding human safety.

The most useful set of evidence when evaluating claims regarding peptidic serum remains therefore simple:

defined formulation + appropriate comparator group + appropriate measurement + transparent presentation of uncertainty.

Neither the number of peptides nor the term „booster” replace this information.

Practical checklist for evaluating serum peptide levels

Before accepting the claim regarding peptide serum, it is worth asking a few questions.

1. What exactly are the peptides present in the product?

The very term „peptidic serum” is too broad.

2. Is this a multi-component formulation?

If the product contains niacinamide, retinoids, hyaluronic acid, acids or other active substances, their potential contribution to the observed effect must be taken into account.

3. What does the declared percentage actually mean?

It is worth determining whether it refers to a pure peptide, a raw material solution, or the entire patented complex.

4. Was the finished product tested?

Ingredient research and product testing answer other questions.

5. Has an appropriate comparison group been used?

The controlled-environment study provides information other than the uncontrolled comparison before and after the use of the product.

6. Is penetration demonstrated if the proposed mechanism requires deep delivery?

The product's own consistency or the encapsulation itself do not confirm this.[9][10][11]

7. What result was measured?

Moisture content, the appearance of wrinkles, markers of collagen and participants' satisfaction should be treated as separate endpoints.

8. How large and how long was the study?

A small, short-term study does not confirm lasting effects or universal safety.

9. Was the study randomized or blinded?

Open-label studies can still be valuable, but their ability to establish a causal relationship is more limited.

10. Is the marketing claim broader than the experiment itself?

The scope of the application should correspond to what was actually examined.

Frequently asked questions

1. What does „multi-peptide” mean?

„Multi-peptide” means that the formulation contains more than one peptide component. However, it does not define a standardized mixture, concentration, mechanism, or expected effect. Two products can contain completely different peptide sequences, amounts, modifications, and bases, even though both are described as multi-peptidic. The study of serum containing 10 peptides concerned a specific formulation, not the entire category of multi-peptide products. [3] Its open design also did not allow for determining the independent contribution of each peptide. Therefore, this term should be treated primarily as information about the composition and then analyzed the evidence regarding the specific product.

2. Does a higher number of peptides mean a better product?

No. A higher number of peptide components does not automatically mean a stronger or more useful effect. Demonstrating such a relationship would require appropriate comparisons between similar formulations containing different numbers of peptides. A study of serum containing 10 peptides did not compare the product with corresponding versions containing one, three, six, or nine peptides. [3] Therefore, it cannot confirm the relationship between the number of peptides and efficacy. Their identity, concentration, stability, formulation, penetration—if relevant—and results from controlled human studies provide significantly more information.

3. Does a peptide serum always contain more peptides than a cream?

No. „Serum” and „cream” describe categories of formulations, not standardized concentrations of peptides. A light serum may contain less peptide than a cream, more peptide, or a completely different set of peptide ingredients. Analytical studies of palmitoylethanolamide peptides show that the actual content can be directly measured in cosmetic matrices. [6] However, even a known concentration does not in itself confirm effective delivery or clinical efficacy. Comparing the actual composition to the specific product’s studies is therefore more useful than assuming that a lighter formulation must be stronger.

4. Can the peptide at the end of the list of ingredients not work?

No. The position on the ingredient list does not allow one to independently determine efficacy. The U.S. FDA labeling regulations for cosmetics include provisions that affect the order of ingredients present in a concentration of 1% or lower, which limits the ability to draw precise quantitative conclusions based solely on the position on the list itself. [4] Furthermore, activity depends on the specific molecule, concentration, formulation, stability, and biological exposure, and not solely on the presence of a large amount of the ingredient. The INCI list may indicate a peptide, but it usually does not specify its exact amount or its role in the action of the finished product.

5. Does „10% peptide complex” mean 10% pure peptides?

It does not have to. The percentage value referring to the peptide complex may describe the entire raw material mixture, not just the pure peptide molecules. Such a complex may contain the peptide along with water, solvents, stabilizers, or other substances. The significance of the declaration depends on what the manufacturer defines as a „complex.” Analytical studies show the difference between direct determination of the peptide content and the mere statement of the presence of a peptide-containing component in the formulation.[6] Without a quantitative specification or the result of the analysis, one should not assume an exact concentration of pure peptide based on the percentage on the packaging alone.

6. Does the peptide skin booster differ from a regular serum?

It may differ in formulation or the intended place in the care routine, but the term „booster” does not create a separate scientific category. It also does not prove that other cosmetics become more effective after its use. Studies of entire routines may show changes when products are used together without isolating the contribution of the additional serum. [16] To demonstrate a real „boosting” effect, the same routine should be compared with the product with and without it. The composition and studies of a specific product are therefore more important than its marketing name.

7. Is there a scientifically proven order of administration for all peptide serums?

No. The evidence discussed does not indicate a universally best order of use for all peptide serums. Studies evaluate specific products under specific conditions, whereas manufacturers provide instructions for their own formulations. The study combining a serum with hyaluronic acid and a peptide-rich cream covered the entire routine, not a comparison of different application orders. [17] Therefore, it cannot confirm the universal rule of „first serum, then cream” or any other scheme for all products. Claims of superiority based on a specific order require studies specifically designed to compare them.

8. Does the light consistency of the serum mean that the peptides penetrate deeper?

No. The light consistency describes primarily the physical and sensory properties of the product. It does not confirm the delivery of the peptide to the living layers of the skin. Penetration depends on the properties of the molecule, the formulation, stability, and the skin barrier. Analytical methods developed for the determination of hexapeptides in various skin-related matrices show why penetration must be measured in the appropriate layers. [11] Even the availability of such a method does not prove that a specific serum achieves biologically significant penetration. Therefore, superficial and deep delivery should remain separate concepts.

9. Does „liposomal” mean that the peptide serum reaches the dermis?

No. The liposomal delivery system describes a formulation strategy, not a confirmed target site. It remains to be determined where the peptide reaches, whether it remains intact, what its concentration is in the individual layers, and whether the achieved exposure has biological significance. A review of liposomal GHK-Cu points to limitations in the available data regarding permeation and the need for appropriate analytical evaluation. [10] Encapsulation can influence the behavior of the formulation, but the mere designation „liposomal” does not confirm delivery of the peptide to the target skin.

10. Can peptide serum improve hydration without confirming collagen production?

Yes. Hydration and collagen production are different biological and cosmetic outcomes. Serum can increase measured hydration and make the skin appear smoother without showing an increase in collagen synthesis. In a randomized pilot study, serum containing niacinamide, postbiotics, and peptides was evaluated for hydration among other things in a multi-ingredient formulation [7]. The results cannot be attributed solely to the peptides; the improvement in hydration should not be taken as evidence of collagen synthesis. The benefit regarding hydration may be significant, but it supports a narrower claim than structural skin remodeling.

11. Does the study of serum containing retinoids and peptides prove the activity of peptides?

No. The multi-component formulation does not allow the participation of a single component to be isolated if the study design was not specifically prepared for this. The retinaldehyde serum studied also contained peptides, ceramides, lipids, and other components of the formulation, and after its use, certain changes were described. [14] The results refer to the finished product. They do not independently prove that the peptides were responsible for the improvement or that they increased the tolerance to retinaldehyde. A more detailed answer would be provided by comparing the corresponding formulations with and without the peptide component.

12. Is an open-label serum study useless?

No. Open-label studies can provide useful information about changes observed during product use, acceptance, tolerance, and performance in real-world conditions. Their main limitations relate to establishing causality and susceptibility to the influence of participant and assessor expectations. A study of serum from 10 peptides provides information about a specific formulation, but did not include a group using the same vehicle or a similar routine without the studied serum. [3] Therefore, it does not eliminate all alternative explanations. Such a study may be valuable, although stronger causal claims require better-controlled designs.

13. Does „clinically tested” mean that the serum was better than the placebo?

No. The term „clinically tested” does not describe a human-participant study. It can refer to both an uncontrolled commercial study and a randomized controlled trial under controlled conditions. For example, a publication on the peptide-pro complex included a section involving human participants in which the participants were compared with their own baseline status, although separate ex vivo experiments included controlled comparisons. [2] To assess the significance of the term „clinically tested,” one must therefore examine the actual methodology, the comparison group, the sample size, and the measured results.

14. Can a serum and cream test show that it is best to use both products?

Only when the project directly compares their use together with corresponding products used separately. In a 12-week study, serum with hyaluronic acid and a peptide-rich cream were described to show changes during joint use in 17 people who completed the study. [17] Since the results were compared primarily with the baseline condition, rather than with separate groups using only serum or cream, it cannot be concluded that either product was necessary or that the combination was more effective. The evidence regarding the combined routine should remain evidence regarding that routine.

15. Does the peptide serum work the same way as the botulinum toxin in an injection?

Such equivalence has not been demonstrated in the evidence discussed herein. The proposed neuro-neurotransmitter-related action requires confirmation of appropriate delivery and biological activity, not merely an improvement in the appearance of fine lines. A review of acetyl hexapeptide-8 indicates uncertainty regarding access to appropriate biological sites and the full local mechanism of action. [9] The cosmetic effect should therefore not be automatically interpreted as an action similar to injections. Terms such as „Botox-like” require evidence and do not in themselves constitute confirmation of equivalence with botulinum toxin.

16. Can a short study confirm the long-term or lasting safety of the results?

No. The direct study only supports observations within the boundaries of the studied population, duration, and observation period. Eight- or twelve-week experiments do not confirm the durability of the benefits after discontinuation of the product if participants are not subsequently observed. Small trials also have limited ability to detect rare adverse effects. Several of the discussed serum studies include relatively short periods and limited populations. [3] [7] Therefore, the results should not be generalized to claims of sustained efficacy, long-term effectiveness, or universal tolerance.

17. What evidence is strongest for a specific claim regarding peptydic serum?

The most direct are usually well-described studies of the actual formulation, using a control group and a endpoint appropriate to the given claim. Experiments on the component itself can support the mechanism, and penetration studies answer questions about delivery, but none of these types of evidence alone confirms the apparent action of the finished cosmetic product. A publication combining ex vivo studies with two clinical trials shows why the individual experimental parts must be interpreted separately. [13] The strongest interpretation combines the claim with a study that directly tested it, retaining information about the sample size, comparator, duration, and uncertainty.

18. Does a higher percentage automatically mean better peptide serum?

No. A higher percentage value does not automatically mean greater effectiveness. First, the percentage may refer to a patented complex rather than a pure peptide. Second, biological activity depends on, among other things, the identity of the peptide, stability, formulation, penetration, and the relationship between concentration and activity. Chemical analysis can determine the amount of peptide in a product, but by itself it does not confirm that the component reaches its intended target or produces a significant cosmetic effect. [6] The percentage value should therefore be interpreted in conjunction with information about what it specifically refers to and with evidence regarding the specific product.

19. Can two serums containing the same peptide work differently?

Yes. The presence of the same peptide component does not mean that two formulations are equivalent. Differences in concentration, pH, solvents, emulsifiers, stabilizers, other active ingredients, packaging, and chemical stability can affect the peptide’s behavior. Studies of acetyl hexapeptide-8 show why the chemical state and analytical characteristics of the component can be important in a finished cosmetic. [8] Therefore, evidence regarding one serum should not be automatically transferred to another product just because both list the same peptide on the list of ingredients.

20. Does the detection of the peptide in the skin prove that the serum is effective?

No. The detection of a peptide answers an important question regarding delivery, but it does not close the entire chain of evidence. It remains necessary to determine whether the detected material is intact peptide, what layer of the skin it resides in, what its quantity is, whether exposure is of biological significance, and whether the proposed effect occurs. Analytical methods that enable the detection of peptides in various matrices associated with skin research are tools for delivery testing. [11] Demonstrating a visible or functional effect in humans remains a separate question requiring the appropriate type of research.

Limitations of evidence regarding peptide serum

„Peptide serum” is a very broad category. Individual products can contain completely different peptide sequences, concentrations, chemical modifications, and auxiliary ingredients, so the results of one product cannot be automatically transferred to the entire category.

Multicomponent formulations further complicate the assignment of the observed effects to a specific component. Improvements following the use of a serum containing peptides together with niacinamide, retinoids, ceramides, humectants, or other active substances should not be automatically attributed to the peptides themselves.[7][14]

Open-label studies and comparisons with baseline conditions can provide valuable information, but they are less capable of establishing causality than properly controlled experiments. [2] [3] Similarly, laboratory and human data should remain separate. A controlled ex vivo experiment does not alter the uncontrolled part involving humans in a randomized clinical trial. [2] [13]

Skin penetration remains an important mechanistic question for some of the claims regarding peptides. The light consistency, rapid surface absorption, or liposomal formulation do not independently confirm delivery to the living layers of the skin.[9][10][11]

Percent declarations can also be ambiguous, because the percentage referring to the peptide complex does not necessarily correspond to the content of the pure peptide. However, the number of peptides does not indicate synergy or advantage. A formulation with 10 peptides should not be considered more effective than a product with one peptide without appropriate comparative testing.[3]

The product format also does not determine effectiveness. Serum, cream, ampoule and booster do not represent additional levels on a universal scale of effectiveness.

The short observation period also limits conclusions regarding durability. The improvement observed during eight or twelve weeks of use does not indicate that the effect will persist after discontinuation of the product.

Ultimately, evidence regarding a product should remain specific to that product. A positive study of one ready-made serum does not confirm the effectiveness of every cosmetic containing the same peptide, nor of all products labeled as „peptide serum.”.

Summary

Peptide serums constitute a diverse group of cosmetic formulations, rather than a single standardized product type.

They can vary significantly in terms of identity and number of peptides, their concentrations, chemical modifications, vehicle, stability, delivery system, other active ingredients, and the quality of the available evidence.

Controlled and uncontrolled human studies described improvements in selected parameters after the use of certain serums and other formulations containing peptides. However, the significance of these results depends largely on the design of the study.

A positive multi-component serum study primarily tells something about the tested finished formulation. It does not automatically prove that the peptides were responsible for every improvement; each peptide had a significant contribution; a higher number of peptides is more beneficial; the declared percentage means a pure peptide; the product penetrates deep into the skin; nor that other serums containing similar ingredients will provide the same result.

Therefore, it is worth keeping a few simple distinctions in mind:

multi-peptide ≠ proven synergy;

serum ≠ higher concentration;

light consistency ≠ deeper penetration;

Liposomal = not confirmed delivery to the epidermis;

clinically tested ≠ placebo-controlled study;

improvement of hydration ≠ collagen synthesis;

improvement after using the product ≠ isolated effect of the peptide.

The most useful evaluation of a peptide serum should therefore take into account the identity of the peptide, the complete formulation, the actual concentration — if known — stability, data regarding delivery where relevant, the study design, the comparator group, and the actually measured result.

This approach allows us to discuss research on peptide serums without discarding valuable results, but at the same time without extending them beyond what has actually been demonstrated.

Disclaimer

The article is purely educational and scientifically informational in nature. It discusses peptide cosmetic ingredients, the science of formulations, analytical testing, issues related to skin penetration, product declarations, and human studies. It does not constitute medical or dermatological advice, diagnosis, treatment recommendations, or recommendations for the purchase or use of a specific peptide serum or other cosmetic product.

Results regarding a single peptide, concentration, formulation, delivery system, study population, or care routine should not be automatically transferred to other products. Individuals with persistent skin problems, significant irritation, known allergies, or other dermatological issues should consult with a suitably qualified specialist.

References

1. Draelos, Z. D. (2018). The science behind skin care: Moisturizers. Journal of Cosmetic Dermatology, 17(2), 138–144. https://doi.org/10.1111/jocd.12490
2. Moy, M., Diaz, I., Lesniak, E., & Giancola, G. (2023). Peptide-pro complex serum: Investigating effects on aged skin. Journal of Cosmetic Dermatology, 22(1), 267–274. https://doi.org/10.1111/jocd.14992
3. Cayce, K., Jacobs, K. M., & Boda, S. (2026). An open-label study to assess the efficacy and tolerability of a multifunctional, 10-peptide face and neck serum to address skin quality. Journal of Cosmetic Dermatology, 25(3), Article e70746. https://doi.org/10.1111/jocd.70746
4. U.S. Food and Drug Administration. (n.d.). Summary of cosmetics labeling requirements. Retrieved September 20, 2026, from Summary of cosmetics labeling requirements
5. Robinson, L. R., Fitzgerald, N. C., Doughty, D. G., Dawes, N. C., Berge, C. A., & Bissett, D. L. (2005). Topical palmitoyl pentapeptide provides improvement in photoaged human facial skin. International Journal of Cosmetic Science, 27(3), 155–160. https://doi.org/10.1111/j.1467-2494.2005.00261.x
6. Chirita, R. I., Chaimbault, P., Archambault, J. C., Robert, I., & Elfakir, C. (2009). Development of a LC-MS/MS method to monitor palmitoyl peptides content in anti-wrinkle cosmetics. Analytica Chimica Acta, 641(1–2), 95–100. https://doi.org/10.1016/j.aca.2009.03.015
7. Rusic, D., Ivic, M., Slugan, A., Leskur, D., Modun, D., Durdov, T., Vukovic, D., Bukic, J., Bozic, J., & Seselja Perisin, A. (2024). Pilot study on the effects of a cosmetic serum containing niacinamide, postbiotics, and peptides on facial skin in healthy participants: A randomized controlled trial. Life, 14(12), Article 1677. https://doi.org/10.3390/life14121677
8. Kluczyk, A., Ludwiczak, J., Modzel, M., Kuczer, M., Cebrat, M., Biernat, M., & Bąchor, R. (2021). Argireline: Needle-free Botox as analytical challenge. Chemistry & Biodiversity, 18(3), Article e2000992. https://doi.org/10.1002/cbdv.202000992
9. Zdrada-Nowak, J., Surgiel-Gemza, A., & Szatkowska, M. (2025). Acetyl hexapeptide-8 in cosmeceuticals—A review of skin permeability and efficacy. International Journal of Molecular Sciences, 26(12), Article 5722. https://doi.org/10.3390/ijms26125722
10. Ogórek, K., Nowak, K., Wadych, E., Ruzik, L., Timerbaev, A. R., & Matczuk, M. (2025). Are we ready to measure skin permeation of modern anti-ageing GHK-Cu tripeptide encapsulated in liposomes? Molecules, 30(1), Article 136. https://doi.org/10.3390/molecules30010136
11. Zhou, W., Wang, P. G., Ogunsola, O. A., & Kraeling, M. E. (2013). Rapid determination of hexapeptides by hydrophilic interaction LC-MS/MS for in vitro skin-penetration studies. Bioanalysis, 5(11), 1353–1362. https://doi.org/10.4155/bio.13.60
12. Jiang, F., Wu, Y., Liu, Z., Hong, M., & Huang, Y. (2023). Synergy of GHK-Cu and hyaluronic acid on collagen IV upregulation via fibroblast and ex-vivo skin tests. Journal of Cosmetic Dermatology, 22(9), 2598–2604. https://doi.org/10.1111/jocd.15763
13. Zhu, M., He, X., Zhu, Z., Lynch, S., Wang, H., Zhou, X., Tu, Y., Steel, A., Hsu, K. C., Niu, Y., Cho, A., Hashimoto, M., Yan, X., Su, M., & Wang, W. (2026). The effect of a serum containing acetyl hexapeptide-8, dipeptide diaminobutyroyl benzylamide diacetate, and gluconolactone on skin biomarkers, wrinkles, and skin texture: Ex vivo and clinical studies. International Journal of Cosmetic Science. Advance online publication. https://doi.org/10.1111/ics.70087
14. Konisky, H., Bowe, W. P., Yang, P., & Kobets, K. (2024). The clinical efficacy and tolerability of a novel retinaldehyde serum with firming peptides to improve skin texture and signs of photoaging. Journal of Drugs in Dermatology, 23(11), 992–997. https://pubmed.ncbi.nlm.nih.gov/39496127/
15. Chang, H., Tao, K., Yang, Y., Wang, Y., Ge, M., Wang, X., Tang, S., & Yu, H. (2025). Novel cyclized hexapeptide-9 outperforms retinol against skin aging: A randomized, double-blinded, active- and vehicle-controlled clinical trial. Journal of Cosmetic Dermatology, 24(7), Article e70290. https://doi.org/10.1111/jocd.70290
16. Draelos, Z. D., Kononov, T., & Fox, T. (2016). An open label clinical trial of a peptide treatment serum and supporting regimen designed to improve the appearance of aging facial skin. Journal of Drugs in Dermatology, 15(9), 1100–1106. https://pubmed.ncbi.nlm.nih.gov/27602972/
17. Gold, M. H., Biron, J. A., Wilson, A., & Nelson, D. B. (2022). Efficacy and tolerability of a hyaluronic acid-based serum and a peptide-rich cream for the face and neck in subjects with photodamaged skin. Journal of Cosmetic Dermatology, 21(8), 3458–3463. https://doi.org/10.1111/jocd.14981
18. Bjerke, D. L., Li, J., Gao, Y., Hu, P., Lintner, K., & Hakozaki, T. (2026). A framework for the safety evaluation of peptides in cosmetics. Current Research in Toxicology, 10, Article 100291. https://doi.org/10.1016/j.crtox.2026.100291