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, gel, light gel serum, or emulsion. It usually also contains other ingredients that affect hydration, consistency, stability, product spreadability, and skin feel.

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

Research on 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 studies answers different scientific questions, and therefore they should not be treated as equivalent.

A human clinical trial may show changes after applying 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 greater 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, the evaluation of evidence regarding a peptide serum should begin with the entire formulation rather than the word „peptide” itself.

The most important questions are:

• What 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?
• Was an appropriate comparison group used?
• What parameters were measured?
• Has percutaneous penetration been demonstrated if the proposed mechanism requires it?

Terms such as „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.

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 tell us 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 its concentration is high. Similarly, a light formula is not proof of deep skin penetration.

Peptides are molecules built from amino acids. Their sequences and chemical modifications can affect, among other things, interactions with other substances, stability, solubility, and behavior 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 fatty acid-derived group attached, while acetylated peptides have a different chemical modification. Such information helps characterize 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, because the base itself can affect the product's performance.

Humectants, emollients, solvents, film-forming agents, and other formulation ingredients can affect hydration, smoothness, elasticity, skin feel, surface appearance, and light reflection—regardless of the peptide's proposed mechanism of action. The science of moisturizers considers both the direct effects 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 result primarily from the moisturizing 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, while the proposed cellular response may require a completely different type of experimental evidence.

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

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, proprietary mixtures, or more complex compositions that also include 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 proprietary „peptide-pro complex,” which is a mixture of neuropeptides, proteins, amino acids, and marine extracts. The study included ex vivo experiments and a 12-week human trial, in which the results were compared to the participants' baseline. [2]

The results therefore apply to this specific mixture, this formulation, and these experimental conditions. They do not allow for the isolation of a single peptide 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 analyzing studies 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 formulations, and the limitations of the evidence can be found in the article Peptides in skincare: effects, formulation, and scientific evidence.

„Booster” primarily describes product positioning

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

However, the word „booster” alone does not mean that the product increases the penetration of other cosmetics, enhances the efficacy of another active ingredient, works synergistically with a moisturizer, 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 alone 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.

In an open-label study, 48 participants used a face and neck serum containing 10 peptides for 12 weeks. Participants were divided according to their previous skincare routines, and the researchers reported improvements in selected skin quality parameters. [3]

However, this was not a randomized comparison of 10 peptides versus 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 ingredient name

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

However, numbers appearing in cosmetic peptide names can be easily 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 present in the product.

On the other hand, the marketing term „blend of six peptides” usually refers to the claimed number of peptide ingredients. Therefore, these numbers describe completely different characteristics.

Scientific terminology and cosmetic nomenclature may also differ. When comparing a product to 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 outlines the general rule of listing cosmetic ingredients in descending order, while providing exceptions for, among others, ingredients present at a concentration of 1% or less and color additives. Other jurisdictions have their own rules that must be evaluated separately.

Therefore, a peptide located at the end of the ingredient list is not automatically ineffective. At the same time, the fact that one peptide is higher than another does not allow for determining their exact quantitative ratio.

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

Research on some peptides was conducted at relatively low concentrations. However, this does not mean that the right 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 tested for a specific effect?”.

In a well-known palmitoyl pentapeptide study, a moisturizer containing this peptide was compared to its peptide-free counterpart, 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 necessarily mean the percentage of pure peptide

Percentage declarations require particularly careful interpretation.

Let's imagine a label that reads "10% peptide complex." This does not necessarily mean that 10% of the finished product consists of pure peptide molecules.

Each percentage value requires specifying what exactly is in the numerator and the denominator. The given amount may refer to the pure peptide, raw material solution, proprietary blend, or a preparation containing the peptide together with water, a solvent, and other ingredients.

These are not equivalent values.

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

This is a general rule regarding composition and does not mean that a specific manufacturer has mislabeled 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 using 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, among others, glycerin, hyaluronic acid, niacinamide, ceramides, plant extracts, exfoliating ingredients, antioxidants, oils, silicones, polymers, preservatives, and texture-modifying substances.

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

For example, 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. However, it changes the scope of conclusions that can be drawn from it.

A randomized pilot study evaluated a serum containing niacinamide, postbiotics, and peptides in 25 participants over four weeks. [7] Among the evaluated parameters, a difference in hydration was noted 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 to conclude that the peptides alone were responsible for the hydration effect.

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

Formulation and declared effects

The substrate affects the availability and action of 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, light exposure, storage method, and the distribution of the peptide in the formulation may matter.

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

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

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

This does not mean that every peptide serum undergoes significant degradation, nor that every oxidized form of a peptide is harmful. The conclusion is much narrower: the name of an ingredient 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 imply deep delivery

One of the common assumptions about serums is the belief that the lightweight texture allows the ingredients to penetrate deeper into the skin.

However, consistency and penetration are not the same property.

A thin 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 of the epidermis constitutes a significant barrier. Peptide penetration may depend on the size and charge of the molecule, hydrophilicity, lipid affinity, chemical modifications, stability, and the overall formulation.

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

Similarly, encapsulation is a formulation strategy rather than proof of destination. A review of liposomal GHK-Cu highlights the limitations of available penetration evidence and the need for appropriate analytical methods. [10]

That is why „liposomal” does not automatically mean „reaches the dermis.”.

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

A validated LC-MS/MS method developed for the quantification of hexapeptides in skin research-related matrices 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 skin layer.

Detection of the peptide does not imply biologically significant exposure

Even if the peptide is detected in a specific skin layer, 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 mean a biologically sufficient exposure.

In the case of the strong mechanist thesis, the chain of proof may look as follows:

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

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

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

Hydration, smoothing, and the impact on collagen are different outcomes.

A peptide serum can be evaluated for moisturization, wrinkle appearance, roughness, elasticity-related parameters, firmness, standardized 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 remodeling.

The study on GHK-Cu with hyaluronic acid described results regarding collagen IV in fibroblasts and ex vivo skin. [12] This is useful mechanistic data, but it does not prove that every serum with 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 about expression wrinkles require their own evidence

Some peptide serums are promoted in the context of influencing signaling related to facial expressions.

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

If the proposed mechanism involves a specific neuronal or neuromuscular site, it should be determined 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 to the claimed result in humans.

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

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

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

How are ready-made serum tests evaluated?

First, determine what question was actually being investigated

The testing of the finished product concerns a specific formulation used under specific conditions. Its significance depends, among 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 to a vehicle, serum compared to another active product, serum added to an existing routine, or serum as one of the elements of a completely 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, on the other hand, 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.

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

Separate the laboratory part from human research

A single publication may cover several different types of experiments, for example, cell 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, while the human part involved comparing participants with their own condition before starting the product use.

These are two different research projects. A controlled laboratory comparison does not turn the human portion into a randomized head-to-head clinical trial.

Similarly, a 2026 publication analyzed 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 subjects, but did not confirm a randomized 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 comparison group and other components

A proper 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, moisturizing ingredients, retinoid, niacinamide, another active substance, the entire combination, or factors unrelated to the product.

Thirty-two women participated in an 8-week study of a serum containing retinaldehyde, peptides, ceramides, and lipids. The results regarding skin appearance and tolerability were reported. [14]

Because the product contained a retinoid, peptides, ceramides, lipids, and other formulation components, the results pertain 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, other comparisons would be needed.

Even a study with an active comparator requires careful interpretation. In a 56-day experiment, 0.0021 TP30T of cyclized hexapeptide-9, 0.0021 TP30T of retinol, and a control were compared. [15]

The results apply to specific formulations and concentrations. The same percentages do not imply equivalent biological activity, and a single formulation containing 0.002% retinol does not represent all retinol cosmetics.

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

Sample size, observation time and uncertainty must be evaluated together

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

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

Statistical significance should be analyzed together with effect size, confidence intervals — if presented — measurement variability, the response of the comparison group, the magnitude of changes at baseline, and the practical significance of the result.

A statistically detectable difference can be small. On the other hand, participant satisfaction may depend not only on visible changes, but also on consistency, scent, spreadability, moisturizing 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 standardized conditions, whether evaluators were blinded where possible, and which outcomes were specified before the analysis began.

What do selected serum studies actually show?

The sources for the respective rows are [7], [3], [2], [14] and [13].

These studies show various types of evidence regarding peptide serums. They do not constitute a ranking of all products or a full review of all research on peptides in skin care.

Skincare routine, multi-peptides and different product formats

Claims regarding routine require comparing entire routines

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

The presented studies do not confirm such a universal rule.

The application conditions used in the study determine what the scientists tested. The manufacturer's instructions, on the other hand, specify how to use a specific product. Neither of these elements automatically establishes the best regimen for all peptide serums.

To determine if adding a serum improves an existing routine, it would be valuable to compare the same routine without the serum and with the serum, while keeping other conditions similar.

If participants introduce several new products simultaneously, the study evaluates the entire combination.

In a 14-week open-label study, a peptide serum used alongside a supportive skincare routine was evaluated in 29 women. [16] Improvements in parameters related to the appearance of the skin were observed.

However, because the intervention included several elements, it is not possible to point to the serum itself, the peptides, or any other element of the routine as the sole cause of the observed changes.

In another 12-week study, a hyaluronic acid serum used together with a peptide-rich cream was evaluated. The study was completed by 17 subjects. [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 of them used separately.

„Multi-peptide describes the composition, not proven synergy

A multi-peptide serum contains more than one peptide ingredient. However, this term does not indicate which exact peptides were used, how much of each is in the product, what proportions they occur in, what their stability, penetration ability, or mechanism of action is.

Two products described as a „10-peptide serum” can therefore have completely different formulations. One may contain ten defined synthetic peptides, while the other may count ingredients found in patented blends. Their concentrations and bases can also differ significantly.

An even stronger statement is „synergy.” It means that the combination of ingredients produces an effect greater than expected based on the action of the individual components in a corresponding comparison.

Merely observing an improvement after applying the mixture does not confirm synergy.

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

The 10-peptide serum study did not compare corresponding products containing a single peptide, multiple peptides, ten peptides, and no peptides. [3] Therefore, it does not allow for creating an efficacy 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, while many serums are a lighter liquid or gel.

Such differences can affect spreadability, occlusion, evaporation, surface residue, moisturizing effect, and skin feel. However, they do not establish a universal ranking of peptide concentration, penetration, potency, or efficacy.

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

If the 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 a hyaluronic acid serum was used together with a peptide-rich cream 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 measures of potency.

Tolerance depends on the entire formulation

Tolerance of a peptide serum depends on the entire formulation, concentration, frequency and time of exposure, application site, and the characteristics of the individuals using the product.

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

A safety assessment framework for cosmetic peptides, which also includes computational methods to support safety analysis, has been proposed. [18] Such tools can be helpful in research, but they do not replace experimental data, product-specific evaluation, or relevant human safety information.

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

defined formulation + appropriate comparison group + proper measurement + clear presentation of uncertainty.

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

Practical checklist for evaluating a peptide serum

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

1. What exact peptides are in the product?

The term „peptide serum” itself is too broad.

2. Is this a multi-ingredient formulation?

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

3. What does the declared percentage actually mean?

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

4. Was the finished product tested?

Ingredient testing and product testing answer different questions.

5. Was an appropriate comparison group used?

A vehicle-controlled study provides different information than an uncontrolled before-and-after product comparison.

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

The consistency of the product itself or its encapsulation does not confirm this. [9] [10] [11]

7. What result was measured?

Hydration, wrinkle appearance, collagen biomarkers, and participant 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 tested.

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 may contain completely different peptide sequences, amounts, modifications, and carriers, even though both are described as “multi-peptide.” The study of the serum containing 10 peptides pertained to one specific formulation, not the entire category of multi-peptide products. [3] Furthermore, its open-label design did not allow for the determination of each peptide’s independent contribution. Therefore, this term should be treated primarily as information about the composition, and evidence regarding a specific product should then be analyzed.

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

No. A greater number of peptide ingredients does not automatically mean a stronger or more beneficial effect. Demonstrating such a relationship would require appropriate comparisons between similar formulations containing different numbers of peptides. The study of the serum containing 10 peptides did not compare the product with corresponding versions containing one, three, six, or nine peptides. [3] Therefore, it cannot confirm a relationship between the number of peptides and efficacy. Much more information is provided by their identity, concentration, stability, formulation, penetration—if relevant—and the results of controlled human trials.

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

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

4. Could a peptide listed at the end of the ingredients list be ineffective?

No. The position on the ingredient list does not allow you to independently determine effectiveness. U.S. FDA cosmetic labeling rules include regulations affecting the order of ingredients present at a concentration of 1% or lower, which limits the ability to draw precise quantitative conclusions based solely on the list position. [4] Activity also depends on the specific molecule, concentration, formulation, stability, and biological exposure, rather than 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 share in the finished product's action.

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

It doesn't have to. The percentage value referring to the peptide complex may describe the entire raw mixture rather than pure peptide molecules. Such a complex may contain the peptide along with water, solvents, stabilizers, or other substances. The meaning of the declaration depends on what the manufacturer defines as a „complex.” Analytical studies show the difference between directly determining the peptide content and merely stating the presence of a peptide-containing ingredient in the formulation. [6] Without a quantitative specification or analytical result, one should not assume the exact concentration of the pure peptide based solely on the percentage on the packaging.

6. Is a peptide skin booster different from a regular serum?

It may differ in formulation or in the intended place in a skincare routine, but the term „booster” does not constitute a separate scientific category. Nor does it prove that other cosmetics become more effective after its use. Studies of entire skincare routines may show changes when products are used together without isolating the contribution of the additional serum. [16] To demonstrate a genuine „boosting” effect, one would need to properly compare the same routine with and without the product. The composition and research on a specific product are therefore more important than its marketing name.

7. Is there a single, scientifically proven order in which to apply all peptide serums?

No. The evidence discussed does not point to a single, universally best order for applying all peptide serums. Studies evaluate specific products under specific conditions, while manufacturers provide instructions for their own formulations. A study combining a hyaluronic acid serum with a peptide-rich cream focused on the entire skincare routine, not on comparing different application orders. [17] Therefore, it cannot confirm a universal rule of „serum first, then cream” or any other sequence applicable to all products. Claims regarding the superiority of a specific order require studies specifically designed to compare it.

8. Does the serum's light texture mean that the peptides penetrate deeper?

No. The term “light texture” primarily describes the physical and sensory properties of the product. It does not confirm that the peptide is delivered 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 to quantify hexapeptides in various matrices related to skin research demonstrate 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. Surface absorption and deep delivery should therefore remain distinct 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 amounts are present in each layer, and whether the achieved exposure is biologically significant. A review of liposomal GHK-Cu highlights the limitations of existing data on penetration and the need for appropriate analytical evaluation. [10] Encapsulation may affect the stability of the formulation, but the term „liposomal” alone does not confirm delivery of the peptide to the dermis.

10. Can a peptide serum improve hydration without evidence of collagen production?

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

11. Does a study of serum containing a retinoid and peptides prove the effectiveness of the peptides?

No. A multi-ingredient formulation does not allow for the isolation of the effect of a single ingredient unless the study design was specifically tailored for that purpose. The tested serum containing retinaldehyde also contained peptides, ceramides, lipids, and other formulation ingredients, and specific changes were reported following its use. [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 comparison of corresponding formulations with and without the peptide component would provide a more detailed answer.

12. Is an open serum test useless?

No. Open-label studies can provide useful information on changes observed during product use, acceptance, tolerability, and product performance in real-world conditions. Their main limitations relate to establishing causality and susceptibility to the influence of participant and evaluator expectations. The 10-peptide serum study provides information on one specific formulation, but did not include a vehicle-control group or an identical routine without the test serum. [3] Therefore, it does not eliminate all alternative explanations. Such a study can be valuable, although stronger causal claims require better-controlled designs.

13. Does „clinically tested” mean that the serum was more effective than a placebo?

No. The term „clinically tested” does not describe a human study design. It can refer to both an uncontrolled observational study and a randomized controlled trial. For example, the publication on the Peptide-Pro complex included a human component in which participants were compared to their own baseline, even though separate ex vivo experiments involved controlled comparisons. [2] To assess the meaning of the term „clinically tested,” one must therefore examine the actual methodology, the comparison group, the sample size, and the measured outcomes.

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

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

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

This equivalence has not been demonstrated in the evidence discussed. The proposed mechanism involving neurotransmission requires confirmation of adequate delivery and biological activity, rather than merely the improvement in the appearance of fine lines. A review of acetyl hexapeptide-8 indicates uncertainty regarding access to appropriate biological sites and the full mechanism of topical action. [9] Therefore, the cosmetic effect should not be automatically interpreted as an injection-like action. Terms such as „Botox-like” require evidence and do not in themselves constitute proof of equivalence to botulinum toxin.

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

No. The study directly supports observations exclusively within the limits of the studied population, duration, and observation period. Experiments lasting eight or twelve weeks do not confirm the persistence of benefits after discontinuing the product if participants were not observed afterward. Small trials also have a limited ability to detect rare adverse effects. Several of the discussed serum studies cover relatively short periods and limited populations. [3] [7] Therefore, the results should not be extended to claims of sustained effects, multi-year efficacy, or universal tolerability.

17. What is the strongest evidence supporting a specific claim about a peptide serum?

The most direct evidence usually comes from well-documented studies of the actual finished formulation, using a control group and an endpoint relevant to the claim in question. Experiments on the ingredient itself can support the credibility of the mechanism of action, and penetration studies can answer questions about delivery, but neither of these types of evidence alone confirms the observable effect of the finished cosmetic product. A publication combining ex vivo studies with two clinical trials demonstrates why the individual experimental components should be interpreted separately. [13] The strongest interpretation links a claim to the study that directly tested it, while retaining information on sample size, comparator, duration, and uncertainty.

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

No. A higher percentage does not automatically mean greater efficacy. First, the percentage may refer to a patented complex rather than the pure peptide. Second, biological activity depends, among other things, on the peptide's identity, 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 ingredient reaches its intended target or produces a significant cosmetic effect. [6] Therefore, the percentage should be interpreted together with information on what it specifically refers to, as well as evidence concerning the specific product.

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

Yes. The presence of the same peptide ingredient 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 behavior of the peptide. Studies on acetyl hexapeptide-8 demonstrate why the chemical state and analytical characteristics of an ingredient can be significant in a finished cosmetic product. [8] Evidence regarding one serum should therefore not be automatically applied to another product simply because both list the same peptide in their ingredients.

20. Does the detection of a peptide in the skin prove that the serum works?

No. The detection of the peptide answers an important question regarding delivery, but it does not close the entire chain of evidence. It still needs to be determined whether the detected material is an intact peptide, in which layer of the skin it is located, what its quantity is, whether the exposure has biological significance, and whether the proposed effect occurs. Analytical methods enabling the determination of peptides in various matrices related to skin research are tools for studying delivery. [11] Demonstrating a visible or functional effect in humans remains a separate question requiring the appropriate type of research.

Limitations of evidence regarding serum peptides

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

Multi-ingredient formulations further complicate attributing observed effects to a specific ingredient. Improvements following the use of a serum containing peptides combined with niacinamide, retinoids, ceramides, humectants, or other active substances should not be automatically attributed to the peptides alone. [7] [14]

Open-label studies and baseline comparisons can provide valuable information, but they are weaker at establishing causality than properly controlled experiments. [2] [3] Similarly, laboratory data and human data should remain separate. A controlled ex vivo experiment does not turn the uncontrolled human part into a randomized clinical trial. [2] [13]

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

Percentage claims can also be ambiguous, because the percentage referring to a peptide complex does not necessarily correspond to the pure peptide content. Furthermore, the number of peptides does not prove synergy or superiority. A formulation with 10 peptides should not be considered more effective than a single-peptide product without an appropriate comparative study. [3]

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

Furthermore, the short observation period limits conclusions regarding durability. The improvement observed during eight or twelve weeks of use does not prove that the effect will persist after discontinuing the product.

Ultimately, the evidence regarding the product should remain linked to that specific product. A positive study of one finished serum does not confirm the effectiveness of every cosmetic containing the same peptide, nor of all products referred to as peptide serums.

Summary

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

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

Controlled and uncontrolled human studies have reported improvements in selected parameters following the application of certain serums and other peptide-containing formulations. However, the significance of these results depends largely on the study design.

A positive study of a multi-component serum primarily says something about the tested finished formulation. It does not automatically prove that the peptides were responsible for every improvement, that every peptide made a significant contribution, that a higher number of peptides is more beneficial, that the declared percentage means pure peptide, that the product penetrates deeply into the skin, or that another serum containing similar ingredients will provide the same result.

That is why it is worth keeping a few simple distinctions in mind:

multi-peptide ≠ proven synergy;

serum ≠ higher concentration;

light consistency ≠ deeper penetration;

liposomal ≠ confirmed delivery to the dermis;

clinically tested ≠ placebo-controlled study;

improved hydration ≠ collagen synthesis;

improvement after product application ≠ isolated peptide effect.

The most useful evaluation of a peptide serum should therefore consider the peptide identity, complete formulation, actual concentration — if known — stability, delivery data where relevant, study design, comparison group, and the actually measured outcome.

This approach makes it possible to discuss research on peptide serums without dismissing valuable results, while at the same time avoiding extending them beyond what has actually been demonstrated.

Disclaimer

The article is for educational and scientific-informational purposes only. It discusses peptide cosmetic ingredients, formulation science, analytical research, issues related to skin penetration, product claims, and human clinical cosmetic studies. It does not constitute medical or dermatological advice, diagnosis, treatment recommendations, or a recommendation to purchase or use any specific peptide serum or other cosmetic product.

Results for a single peptide, concentration, formulation, delivery system, study population, or skincare routine should not be automatically extrapolated to other products. Individuals with persistent skin concerns, significant irritation, known allergies, or other dermatological conditions should consult 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. Cucumber, K., Nowak, K., Wadych, E., Ruzik, L., Timerbaev, A. R., & Matczuk, M. (2025). Are we ready to measure skin permeation of modern antiaging 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