Peptides for sensitive and acne-prone skin: what do the studies say?

Peptides are ingredients in some cosmetics intended for sensitive, reactive, or acne-prone skin. However, the mere presence of a peptide in the formula does not mean that the finished product is non-irritating, hypoallergenic, non-comedogenic, anti-inflammatory, or that it is effective in treating acne or other skin conditions.

Peptides constitute a chemically very diverse group of molecules. They can differ significantly in amino acid sequence, size, charge, stability, concentration, formulation method, and biological activity. Equally important are the other components of the finished cosmetic product, as they affect what reaches the skin, how the product behaves during application, how stable the peptide remains, and how well the entire formulation is tolerated.

If you want to learn the chemical basics of this group of compounds first, see: Peptides – what they are, how they work and how they are classified.

Available scientific evidence covers very different levels of research, including:

• ingredient and formulation analyses;
• chemical and laboratory experiments;
• antimicrobial activity tests;
• cell culture studies;
• animal models;
• small, uncontrolled human studies;
• vehicle-controlled product studies;
• and randomised clinical trials of specific experimental preparations.

Each of these types of research answers a different question.

A peptide that inhibits bacterial growth in the laboratory has not thereby been proven effective in treating acne in humans. A peptide that influences an inflammatory pathway in cultured cells does not automatically have to alleviate the symptoms of sensitive skin in a human. Conversely, a moisturising cream that improves skin hydration or is well tolerated does not necessarily treat acne, rosacea, eczema, or allergic contact dermatitis.

A reliable assessment should therefore separate at least five issues:

1. skin condition or study population;
2. a specific peptide or a ready-made formulation;
3. route and duration of exposure;
4. measured result;
5. the quality of the comparison used.

Such a distinction makes it possible to describe promising results without attributing them to every cosmetic product labelled as „peptide”.

Sensitive skin and product tolerance

„Sensitive skin” requires an appropriate context

The term „sensitive skin” is commonly used to describe symptoms such as:

• stinging;
• baking;
• itching;
• tightness;
• dryness;
• redness;
• discomfort

after applying products or under the influence of environmental conditions, which might not cause a similar reaction in other people.

However, scientific research does not apply a single universal definition of sensitive skin.

Participants may be qualified on the basis of:

• self-assessment of skin sensitivity;
• responses in questionnaires;
• reaction to a standardised test;
• researcher evaluations;
• or other inclusion criteria.

The way the study population is defined affects the extent to which the results can be generalised to other people.

Sensitive skin is also not automatically the same as:

• allergic contact dermatitis;
• irritant contact dermatitis;
• acne;
• rosacea;
• seborrhoeic dermatitis;
• atopic eczema.

A person may experience more than one of these problems, but these terms should not be used interchangeably.

Therefore, product research should clearly state which population actually took part in it.

A 2021 study analysed 88 facial cosmetics advertised as being formulated for sensitive skin, along with the evidence concerning the peptides identified in these products. The authors noted that a significant proportion of the available material originated from patents and supplier documentation, whereas there were relatively few clinical trials specifically involving volunteers with sensitive skin available in the analysed material. [1]

This was an observation concerning a specific set of products and literature available at the time the analysis was conducted.

It should not be interpreted as a current list of all peptides and all modern cosmetics for sensitive skin.

However, the study shows an important difference:

product marketing for sensitive skin ≠ proven tolerance in an appropriately selected and controlled population.

Sensitive skin does not have a single biological mechanism

Two people who describe their skin as sensitive do not necessarily experience the problem for the same reason.

The symptoms may potentially be influenced by:

• skin barrier dysfunction;
• exposure to irritants;
• contact dermatitis;
• inflammatory skin diseases;
• environmental conditions;
• excessive cleansing;
• simultaneous use of multiple active ingredients;
• individual sensory responses.

Therefore, a peptide product well-tolerated in one sensitive skin study does not necessarily suit every type of hypersensitivity.

The definition of the studied population remains part of the evidence.

Tolerance applies to the entire formulation

Alongside peptides, a finished cosmetic product may contain many other ingredients, such as:

• fragrances;
• preservatives;
• solvents;
• surfactants;
• Acids;
• retinoids;
• plant extracts;
• emollients;
• humectants;
• occlusive ingredients;
• antioxidants;
• other active ingredients.

Each of these elements can affect irritation, allergy, product consistency, ingredient penetration, hydration and overall tolerance.

Good tolerance of the finished cosmetic product does not mean, therefore, that the peptide is responsible for it.

Similarly, the occurrence of a reaction does not automatically prove that it was caused by the peptide component.

FDA information on cosmetic allergens indicates, among other things, the potential importance of fragrances and preservatives in allergic reactions. The FDA also explains that marketing terms such as „hypoallergenic” or „for sensitive skin” do not constitute a federal guarantee of safety or tolerance in the United States. [2]

The practical conclusion is simple:

It is worth analysing the whole formulation, not just the highlighted ingredient.

The product name or a claim on its packaging is not enough to determine how the entire formulation will behave in people with a specific type of skin sensitivity or condition.

Ingredient safety and tolerance of the finished formulation are different questions

The peptide may be well tolerated when investigated on its own or under specific experimental conditions.

However, this does not mean it will behave identically when combined with:

• with acids;
• with retinoids;
• with alcohols;
• fragrances;
• with preservatives;
• penetration enhancers;
• with other ingredients.

Similarly, irritation after using a multi-ingredient product does not prove that the peptide itself is an irritant.

Conclusions concerning the entire formulation require testing of the entire formulation.

„Non-irritating” and „non-comedogenic” answer different questions

Irritation and comedogenicity are two different endpoints.

Irritation refers to a local adverse reaction which may include:

• redness;
• baking;
• stinging;
• dryness;
• discomfort.

Comedogenicity, on the other hand, refers to the tendency to cause or worsen comedones, which are blemishes resulting from blocked hair follicles.

The product can be evaluated against one of these parameters without proving the other.

Similarly, the term „acne-prone skin” is not a measurement of skin sensitivity.

The same person can have both sensitive and acne-prone skin, but a study regarding hydration or comfort does not confirm an anti-acne effect.

Such a distinction prevents the favourable result for one parameter from being extended to several unrelated declarations.

„Hypoallergenic” does not mean that an allergy is impossible

The term „hypoallergenic” can suggest that a product is incapable of causing an allergic reaction.

Such an interpretation goes too far.

Allergic reactions depend on individual sensitisation and exposure.

A marketing term cannot guarantee that every person will tolerate all the ingredients in the product.

Similarly:

dermatologically tested ≠ tolerated by everyone.

formula for sensitive skin ≠ impossibility of an allergy occurring.

peptide product ≠ non-irritating product.

The study design and actual tolerance data are more informative than the label designation alone.

Assessment of sensitive skin may confirm a narrower, specific result

In the study of the peptide derivative acting as the BSFAB protease inhibitor, chemical and laboratory analyses were combined with an evaluation on subjects with self-perceived sensitive skin, conducted under product-substrate control. [3]

The authors described an improvement in stratum corneum barrier integrity and the subjective assessment of healthy skin appearance and condition at the analysed time points. [3]

This is a more concrete type of evidence than the general statement that „peptides are fragile”.

However, the study concerns:

• of a specific modified molecule;
• of a specified formulation;
• of a specific population;
• tangible results.

It does not confirm the universal tolerance of all cosmetic peptides.

Nor is barrier integrity synonymous with a full assessment of all possible symptoms of sensitive skin.

Therefore, the study should be described in accordance with what was actually measured.

Peptides and cosmetic claims regarding acne

Acne encompasses various types of lesions that should be evaluated separately

Acne is not a single, uniform type of skin lesion.

In research, one can separately analyse:

• open blackheads;
• closed comedones;
• lumps;
• spots;
• lumps;
• cysts;
• the number of inflammatory lesions;
• the number of non-inflammatory changes;
• the total number of changes;
• overall clinical severity.

Individual parameters may vary in different directions.

Improving one type of blemish does not automatically mean an improvement in all acne symptoms.

NHS information distinguishes between, among other things, open comedones, closed comedones, papules, pustules, nodules and cysts. [4]

This illustrates why the term „fewer spots” is, from a scientific point of view, incomplete if it is not clear what type of lesions were being assessed.

Acne-prone skin does not necessarily mean clinically diagnosed acne

The term „acne-prone skin” is often used in the cosmetics industry.

A person might describe their skin in this way because imperfections appear on it from time to time.

This is not automatically equivalent to a clinically defined population of people with acne participating in a therapeutic trial.

Therefore, a product that has been assessed for suitability for acne-prone skin should not automatically be presented as a product with proven efficacy in the treatment of acne.

Cosmetic outcomes should not replace clinical outcomes for acne

A cosmetic study may assess:

• moisture;
• over-greasing;
• texture;
• smoothness;
• redness;
• participants’ satisfaction;
• the overall appearance of the skin.

These are valid endpoints.

However, they do not replace measures of change or validated acne severity scales if the claim relates to an improvement in the acne itself.

Antimicrobial activity remains a laboratory finding until it is clinically confirmed

Some peptides are being studied for their effects on microorganisms associated with acne or on specific inflammatory pathways.

These are valid areas of research.

However:

In vitro antibacterial activity ≠ treatment of acne in humans.

The experimental peptide LZ1 demonstrated activity against acne-associated bacteria and showed efficacy in a mouse model of skin colonisation. The study also included a laboratory assessment of cytotoxicity. [5]

These results constitute pre-clinical data justifying further studies.

They do not prove that the peptide gel available to consumers treats acne in humans.

The nomenclature of bacteria has changed, but the scientific question remains the same

In older publications, the name Propionibacterium acnes is sometimes used.

This bacterium is now commonly referred to as Cutibacterium acnes.

Regardless of the terminology used, the inhibition of bacterial growth under laboratory conditions is not equivalent to demonstrating an improvement in the overall clinical picture of acne.

Antimicrobial activity therefore constitutes only one potential element in the entire chain of evidence.

Delivering the peptide to the site of action is important

For an antimicrobial peptide to affect acne after topical application, several additional questions need to be answered:

• Does the peptide remain stable in the formulation?
• Does it reach the appropriate circles?
• Does it retain its biological activity?
• Does it reach the required concentration under realistic exposure conditions?
• Is the formulation well-tolerated?
• Does the observed effect lead to a reduction in clinically significant changes?

The bacterial test only answers part of these questions.

A small peptide study showed different changes in different types of acne lesions

The study of synthetic peptides derived from granulysin included laboratory antimicrobial tests and a 12-week evaluation of the topical application of the preparation in 30 people with facial acne.[6]

The authors described:

• reduction in the number of crusts;
• improvement of the result in the clinical assessment scale;
• an increase in the number of comedones [6]

This mixed result is of great importance.

It would be incorrect to simplify it to say:

„peptides cleanse the skin from acne.”.

The individual types of changes did not change in the same direction.

The abstract of the publication also does not confirm a randomized clinical comparison with the drug formulation.

A more appropriate proposal would be:

The specific experimental formulation provided results that justified further research, taking into account the differences between the types of changes and the limitations of the research project.

Mixed results should not be reduced to one positive headline.

If one parameter improves and the other deteriorates, the whole picture must be presented.

Selective reporting can lead to a false conclusion.

For example:

less spots + more blackheads ≠ overall improvement in all forms of acne.

Multifactorial anti-acne gels do not allow the action of the peptide to be isolated

In a prospective eight-week study, the gel containing:

• ingredients related to retinoids;
• antimicrobial peptide;
• salicylic acid;
• glycolic acid;
• Niacinamide. [7]

25 women were included in the study, and 22 completed the follow-up period.[7]

The authors described a reduction in selected parameters related to acne compared to baseline values.

The study is relevant to the entire combination used.

However, some of the ingredients contained in it could have influenced the observed changes.

On this basis, it is not possible to isolate the activity of the peptide itself.

Evidence regarding combinations refers to combinations

This principle is particularly important in cosmetic research.

If the formulation contains several active ingredients, a positive result indicates the effectiveness of the tested combination under specific conditions.

Does not prove that:

• the effect was attributed to a peptide;
• removing the peptide would eliminate the effect;
• the peptide itself would reproduce the result;
• Another cosmetic containing the same peptide would work similarly.

Assigning an action to a specific peptide requires a properly designed comparison that allows the isolation of this variable.

User reviews answer another question

Consumer reviews can provide information about:

• consistency;
• the smell;
• ease of application;
• mixing with other cosmetics;
• fatness;
• comfort of use;
• subjective feelings.

However, they do not control factors such as the simultaneous use of other products, the natural fluctuations of acne, hormonal changes, clinical diagnosis, regularity of use, environmental conditions, or the user's expectations.

Therefore, the review of a product labeled as „peptide acne gel” does not constitute evidence of the effectiveness of the peptide.

The „before and after” photos also require inspection

Acne can naturally change its severity.

The appearance of the photos is also influenced by:

• lighting;
• camera settings;
• angle of the photo;
• makeup;
• skin hydration;
• image processing.

Standardized photography can be a valuable component of a properly designed study.

However, the uncontrolled images alone do not allow us to determine which component is responsible for the observed change.

Rosacea and eczema: cosmetics and treatment

Similar symptoms do not mean the same disease.

Rosacea, atopic dermatitis, contact dermatitis, seborrheic dermatitis, and acne may have certain common visual or sensory characteristics.

They may include:

• redness;
• bumps or unevenness;
• dryness;
• baking;
• itching;
• pricking.

However, these are different clinical problems.

NHS materials regarding rosacea indicate that it may resemble other diseases and that irritation or tingling may occur when using cosmetics.[8]

NHS information regarding atopic dermatitis describes, among other things, itching, dryness, cracking, and inflammation of the skin.[9]

A product that improves dryness can be useful as a moisturizing preparation.

However, this does not mean that it treats the disease that is the cause of the symptoms.

Improvement of symptoms and modification of the disease are different declarations.

The formulation can improve:

• moisture;
• softness;
• comfort;
• apparent dryness

without affecting the underlying disease process.

This distinction is important in the case of peptide cosmetics, because broad terms such as „relieves inflammatory conditions” can blur the line between cosmetic and therapeutic action.

The actually measured parameter should remain visible in the description.

Naturally occurring peptides are not the same as cosmetic peptides

Peptides naturally present in the human body can participate in, among other things, the following:

• inflammatory processes;
• vascular signaling;
• immune defense;
• sensory reactions;
• tissue regulation.

Studies of these endogenous peptides help to understand the biology of diseases.

However, this does not automatically mean that the use of a cosmetic peptide unrelated to them will produce a specific effect.

A clinical-control study compared the levels of a peptide associated with the calcitonin gene, called CGRP, in the blood of 123 people with rosacea and 68 people in the control group.[10]

Researchers described higher corrected CGRP concentrations in the group with rosacea [10].

This is an observation of a relationship.

This is not a study showing that a cosmetic peptide treats rosacea.

Biological relationship does not automatically indicate the direction of treatment

Even if the level of a specific biomarker differs between people with and without the disease, this does not automatically mean:

• that the marker caused the disease;
• that its reduction will improve the clinical condition;
• that locally applied cosmetics can significantly modify it.

The mechanistic relationship and therapeutic intervention are two different research questions.

LL-37 shows why not all peptides can be attributed to a single function

In another study, LL-37 cathelicidin was analyzed in laboratory models and ex vivo in relation to exposure to UVB. The authors described effects corresponding to increased inflammatory signaling under the tested conditions.[11]

This shows that different peptides can participate in very different biological processes.

Therefore:

Peptide ≠ an automatically anti-inflammatory effect.

At the same time:

Peptide ≠ an automatically inflammatory action.

The interpretation depends on the specific molecule and the experimental conditions.

The results from the mouse model of skin inflammation are not evidence of the efficacy of the cosmetic product in humans

The study of silk peptides described the results obtained in a chemically induced mouse model resembling atopic dermatitis, as well as in cell experiments.[12]

Such a model can be used to test specific immunological hypotheses.

However, it does not confirm the effectiveness of a peptide moisturizing cream in humans.

The differences include, among others:

• species;
• model of the disease;
• type of preparation;
• the method of exposure;
• the dose;
• formulation;
• clinical context.

Therefore, a positive result in an animal study should remain defined as pre-clinical evidence.

„Silk peptides” also do not mean a standardized intervention

Materials derived from silk can vary depending on:

• sources;
• the method of processing;
• hydrolysis;
• particle size;
• composition;
• the formulation.

A positive result for one experimental product does not automatically confirm the effectiveness of every cosmetic labeled as containing silk peptides.

A negative controlled study also provides important evidence.

In a randomized, double-blind study, patients and assessors compared locally applied omignan with ketoconazole and placebo in people with mild or moderate inflammatory facial skin disease of the sebaceous gland [13].

Omiganan was described as well tolerated, but did not show a clinically significant improvement compared to placebo.

The active comparator showed a better result. [13]

Alopecia areata is not the same as:

• rosacea;
• atopic skin inflammation;
• acne.

The study does not therefore determine the effectiveness of all peptides in these diseases.

Its broader methodological significance lies in showing that a justified antimicrobial mechanism does not necessarily lead to clinical benefits automatically.

Negative results help verify mechanistic hypotheses

Preclinical studies often indicate biologically plausible mechanisms.

Clinical studies, however, verify whether these mechanisms translate into significant results under more complex biological conditions.

A negative controlled study can therefore provide very valuable information, even if the previous laboratory justification seemed promising.

Cosmetic and medical claims regarding the treatment of diseases require additional evidence.

The FDA explains that product labeling and claims regarding its activity help in the United States to distinguish cosmetics from medicines and products that meet both definitions.[14]

This is an example of regulation in the USA and does not mean that all jurisdictions apply the same categories.

From the perspective of interpreting evidence, the principle remains useful.

Improved hydration does not prove the treatment of acne.

The improvement in comfort does not prove the control of rosacea.

The change in immune response in mice does not indicate efficacy in the treatment of eczema in humans.

The cosmetic product can support skin comfort without becoming a proven method of treating any inflammatory disease.

Evidence regarding ready-to-use formulations

Start with the population actually covered by the study

The study conducted in healthy volunteers does not automatically confirm the product's suitability for people with:

• active atopic dermatitis;
• Rosacea;
• inflammatory acne;
• allergic contact dermatitis;
• another recognized dermatological problem.

Similarly, a study involving people who declare sensitive skin does not have to represent people with confirmed contact allergy.

The BSFAB study included people who reported having sensitive skin.[3]

Thanks to this, it is more suitable for this population than a general cosmetic examination.

However, Nadal does not confirm universal tolerance.

The inclusion and exclusion criteria are important

The term „tested on sensitive skin” conveys little information unless it is known:

• as defined by sensitivity;
• whether active skin diseases have been excluded;
• whether the participants were taking medication;
• have people with known allergies been excluded;
• how many people completed the survey.

These details determine how widely the results can be interpreted.

The ready-made formulation can improve the result without confirmation that a peptide is responsible for it

In a randomized pilot study, serum containing:

• niacinamide;
• postbiotic organisms;
• peptides

in 25 healthy participants for four weeks. [15]

The authors described, among other things, the difference in skin hydration during the final assessment. [15]

The study provides data regarding this specific combination.

It does not allow the activity of the peptides themselves to be isolated.

It also does not confirm the treatment:

• acne;
• Rosacea;
• eczema;
• another inflammatory skin disease.

Randomization does not always allow determining which component is responsible for the effect.

Randomization can improve the reliability of the comparison between interventions.

However, if several ingredients differ between the tested products at the same time, the study still does not allow determining which of them was responsible for the observed effect.

A suitable research design is needed to assign an action to a specific component.

Adjust the endpoint to match the declaration

The study of granulysin-derived peptides shows why individual types of changes should be analyzed separately.[6]

The study of a multi-component anti-acne gel, however, shows why the improvements achieved through the combination cannot be automatically attributed to the peptide component.[7]

Short-term tolerance does not mean universal security

A small study can provide useful information about common reactions that occur over a short period of time.

However, it has limited detection capabilities:

• rare reactions;
• delayed allergy;
• interactions with other cosmetics;
• long-term effects;
• reactions in populations excluded from the study.

For example, a study of tetrapeptide-68 included 25 women for 12 weeks and did not report any adverse effects.[16]

This is useful information regarding tolerance under certain conditions.

However, it does not constitute proof of universal safety.

„No adverse reactions have been reported” is more accurate than „completely safe”

These statements are not equivalent.

„No adverse reactions were reported in the study,” describes the observation.

„The product is completely safe” is a much broader statement regarding the population and situations that may never have been tested.

The language used to describe the evidence should preserve this distinction.

Safety assessment frameworks do not automatically confirm the safety of every peptide

The proposed approach to the safety assessment of cosmetic peptides includes, among other things, computational methods that can help identify potential issues that require further evaluation.[17]

Such tools can support the research process.

However, they do not automatically confirm the safety of every peptide or ready-made formulation.

The actual exposure and context of the product still matter.

Blindfolding, control groups, and full reporting are important

To subjective results such as:

• comfort;
• softness;
• stinging;
• satisfaction

they can influence the expectations of the participants.

The blindfold can limit some types of errors.

The appropriate control group, however, helps to separate the effects of the intervention being studied from:

• actions of the underlying ground itself;
• natural changes;
• other cosmetics used;
• regression to the mean;
• the expectations of the participants.

The number of people who completed the survey is also important.

25 women were included in the study of a multi-component anti-acne gel, but 22 completed the follow-up. [7]

This difference should remain visible.

The number of people included in the study and the number of participants included in the final analysis are not always the same.

In small studies, the loss of participants can particularly affect interpretation.

Statistical significance is not the whole result

A statistically significant difference does not automatically confirm:

• great clinical benefit;
• the causal relationship with a specific component;
• long-term effect;
• the possibility of transferring the result to another population.

The interpretation should also take into account:

• the magnitude of the effect;
• uncertainty;
• comparator;
• duration of the study;
• consistency of results;
• clinical significance.

How to evaluate a peptide product for sensitive or acne-prone skin?

An organized analysis of the evidence helps distinguish marketing language from what has actually been demonstrated.

1. Determine which peptide was used

Is the ingredient:

• specifically defined peptide sequence;
• modified peptide;
• a mixture of peptides;
• protein hydrolysate;
• element of a protected complex?

2. Check the entire formulation

What other ingredients does the product contain?

If the study concerns a complete formulation, the peptide cannot be interpreted in isolation from the other components.

3. Determine the studied population

Has the study been conducted at:

• healthy volunteers;
• people who declare sensitive skin;
• people with recognized acne;
• Rosacea;
• eczema;
• seborrheic dermatitis;
• another group?

4. Check the measured result

Was it evaluated:

• moisture;
• integrity of the barrier;
• stinging;
• redness;
• spots;
• scales;
• the total number of changes;
• increase in microorganisms;
• severity of the disease?

5. Establish the research model

Do the evidence come from:

• chemical test;
• bacteria breeding;
• human skin cells;
• ex vivo tissues;
• research on mice;
• research involving humans?

6. Check the comparator

Has it been applied:

• placebo;
• the sole substrate;
• another active product;
• only comparison with the initial value;
• no comparator?

7. Check the duration of the study

Several hours of tolerance observation do not allow for determining safety for many months.

Similarly, a short-term laboratory test does not confirm a lasting improvement in the disease.

8. Check whether the peptide’s activity has been isolated

If the formulation contains several active ingredients, it is necessary to check whether the study design allows determining which of them was responsible for the result.

9. Pay attention to mixed or negative results

It is not necessary to analyze only the favorable end point.

A study showing fewer crusts but more scaly patches presents a different picture than a result clearly favorable.[6]

10. Do not go beyond the limits of evidence in your conclusions

Do not confuse:

antimicrobial activity → in the treatment of acne;

moisturizing → in the treatment of eczema;

tolerance of sensitive skin → in the treatment of rosacea;

improvement in the mouse model of skin inflammation → in effectiveness in humans;

Any

improvement after the use of a multi-component formulation → as evidence of the action of the peptide itself.

Irritation and appropriate clinical evaluation

The symptoms require interpretation, not a marketing explanation

Stinging or redness after applying the product does not mean that the peptide is „activating” the skin.

Similarly, the appearance of new changes should not be automatically interpreted as a necessary period of adaptation.

Possible explanations may include:

• irritation;
• an allergic reaction;
• the action of another component;
• an existing skin disease;
• the simultaneous use of multiple products;
• another reason.

The mere presence of the peptide in the composition does not allow us to determine the mechanism.

„Purging” should not be a universal explanation

The appearance of new changes after the start of using a cosmetic product is sometimes referred to as „purging”.

However, this explanation should not be applied automatically to every reaction.

New skin changes can have many causes.

The peptide product does not have to cause an initial deterioration to later provide benefits.

Claims that irritation or the appearance of new changes mean that the cosmetic product is „working” require evidence.

The history of an exhibition can tell more than the product label

When symptoms appear, it is useful to ask:

• What new product was introduced?
• What other cosmetics were used at the same time?
• Where did the symptoms appear?
• How quickly did they appear?
• Did the formulation contain fragrance ingredients, acids, retinoids, or other potentially significant ingredients?
• Did the symptoms persist?

This does not allow one to independently determine the diagnosis.

However, it shows why the immediate assignment of the reactions to „peptides” may be premature.

Clinical tests of cosmetics differ from home testing

Patch tests performed under the supervision of a specialist can be used to diagnose suspected allergic contact dermatitis using specific allergens and to standardize the assessment of reactions over time.

This is not the same as applying a small amount of cosmetics to the skin at home.

The FDA discusses professional evaluation and testing in the event of suspected allergies to cosmetics. [2]

A home trial can provide limited information about immediate tolerance.

However, he does not rule out:

• delayed allergy;
• cumulative irritation;
• the reaction occurring under other exposure conditions.

The reaction to the formulation does not automatically identify the component

If a cosmetic contains 20 ingredients and a reaction occurs after its use, observation indicates that it occurred during the use of the entire formulation.

However, it does not allow you to independently determine which component was responsible.

Identifying a specific component may require a more structured assessment.

Severe acne and persistent symptoms may require professional evaluation

Moderate or severe acne, painful nodules or abscesses, and the risk of scarring may require appropriate clinical evaluation.[4]

Such situations are not solved by simply choosing another cosmetic product labeled as suitable for acne-prone skin.

Similarly, persistent redness or tingling in the face may require evaluation for rosacea or another problem.[8]

Eye pain or visual disturbances associated with suspected rosacea require prompt medical consultation.[8]

In the case of eczema, worsening symptoms or signs of possible infection also belong to problems that require appropriate clinical evaluation.[9]

These examples show why the term „sensitive skin” should not replace a proper assessment of ongoing or aggravated symptoms.

Opinions of other people do not determine individual tolerance

One person's positive experience does not mean that another will tolerate the same product as well.

Similarly, a single negative opinion does not prove that the entire category of peptides is problematic.

Reviews can be useful for evaluating:

• consistency;
• the smell;
• packaging;
• the method of application;
• subjective feelings.

However, clinical claims require a different type of evidence.

The proposal should remain specific

Selected studies support further investigation of specific peptides and formulations.

They include:

• positive results;
• mixed results;
• preclinical mechanisms;
• limited studies involving humans;
• a controlled study that did not demonstrate the expected clinical benefit in the disease being studied.

This does not justify the claim that cosmetic peptides as a whole are automatic:

• non-irritating;
• hypoallergenic;
• non-comedogenic;
• anti-acne;
• effective in rosacea;
• effective in eczema.

The most substantiated proposal should include:

population + peptide or formulation + comparator + result + duration + limitations.

Frequently asked questions

1. Are peptide products automatically non-irritating?

No. The presence of peptides does not mean that every ready-to-use formulation is non-irritating. Other ingredients, their concentration, vehicle, exposure conditions, and individual skin sensitivity also play a role. An analysis of cosmetics intended for sensitive skin showed a limited number of relevant clinical studies supporting many of the evaluated peptide claims.[1] This was a historical analysis and does not describe every contemporary product, but it shows why the presence of a component in a cosmetic product is not the same as demonstrated tolerance. What matters is the entire formulation and the population in which it was actually tested.

2. Does a cosmetic peptide treat acne?

Not automatically. For some experimental peptides, there are preliminary results related to acne, but the studies vary in design and results. In a study of peptides derived from granulysin, fewer pustules were noted, but at the same time more comedones, and the abstract did not indicate a randomized comparison with the product base. [6] Such mixed results do not justify a general claim for all cosmetic peptides. Evaluation of anti-acne efficacy requires studies of a specific formulation with appropriate assessment of changes, severity, comparator, and observation time.

3. Does sensitive skin mean skin allergy?

No. Subjective skin sensitivity and allergic contact dermatitis are not the same thing. Itching, burning, redness, or discomfort can have different causes; however, an allergy involves an immune response to a specific substance. The FDA discusses professional diagnosis in cases of suspected cosmetics allergies.[2] The term „for sensitive skin” does not allow for the cause of symptoms to be determined or for allergies to be ruled out.

4. Does „non-comedogenic” also mean „non-irritating”?

No. These are two different parameters. Comedogenicity refers to the formation or exacerbation of comedones, whereas irritation refers to an unwanted local reaction. A product may be beneficial in one parameter without being confirmed in the other. A study of peptidyl derivatives of granulysin also shows that even individual types of acne can react differently. [6]

5. Does the antibacterial activity in the laboratory prove that the peptide gel removes acne?

No. Antimicrobial activity in the laboratory shows activity under specific experimental conditions. It does not demonstrate clinical anti-acne efficacy. LZ1 showed activity in bacterial experiments and in a mouse model, which constitutes preclinical data. [5] The efficacy of the topical product in humans would require an appropriate formulation, delivery of the ingredient, tolerability, and evaluation of clinical acne changes.

6. Does reducing the number of pimples mean an improvement in any type of acne?

No. The individual types of changes should be analyzed separately. In the study of peptidic derivatives of granulysin, the number of comedones decreased, but the number of blackheads increased. [6] Simplifying this result to state that „the acne improved” would overlook a significant part of the data.

7. Does the effectiveness of a multi-component anti-acne gel prove the action of the peptide contained in it?

No. The improvement after the combination was used does not automatically indicate which component was responsible for it. The gel studied contained ingredients related to retinoids, salicylic acid, glycolic acid, niacinamide, and a antimicrobial peptide.[7] The results refer to this combination. To confirm the effect of the peptide itself, a project would be needed to isolate its effect.

8. Does the improvement in hydration mean that eczema has been cured?

No. Hydration is a specific skin parameter, whereas eczema is a clinical problem that also includes other features. A randomized pilot study of a serum containing niacinamide, postbiotics, and peptides was conducted in healthy participants and reported the results regarding hydration. [15] This was not a study of the treatment of recognized eczema.

9. Do CGRP studies mean that the cosmetic peptide can treat rosacea?

No. The CGRP study compared the concentrations of this naturally occurring peptide in people with rosacea and in the control group. [10] The peptide cosmetic was not studied. The association between the endogenous peptide and the non-related cosmetic ingredient does not indicate that the non-related cosmetic ingredient is responsible for rosacea.

10. Do all peptides have anti-inflammatory effects?

No. Peptides can have very different biological functions. In an experimental study of LL-37, increased inflammatory signaling was described under certain UVB-related conditions.[11] This does not mean that all cosmetic peptides are pro-inflammatory, just as a positive result for another peptide does not mean that all peptides are anti-inflammatory.

11. Does the study of eczema in mice confirm the effectiveness of the peptide cream in humans?

No. Mouse models can be used to study mechanisms and provide preclinical data, but they do not confirm clinical efficacy in humans. The study of silk peptides included an experimentally induced model of changes resembling atopic dermatitis in mice and laboratory studies. [12] The product used in humans may differ in preparation, concentration, formulation, and method of exposure.

12. Did controlled studies of peptides also show a lack of clinical benefit?

Yes. In a randomized, blinded study of inflammatory facial acne, omignan applied topically showed no clinically significant improvement over placebo, although it was described as well tolerated.[13] The active comparator achieved a better result. This does not mean that all peptides are ineffective. It does, however, indicate that the likely antimicrobial mechanism does not guarantee clinical benefit.

13. Does the „for sensitive skin” claim automatically cover rosacea or eczema?

No. Sensitive skin, rosacea, eczema, and contact allergic dermatitis are different populations and different clinical questions. The BSFAB study included a specific group of people who declared themselves sensitive skin and parameters related to the skin barrier. [3] It did not confirm the treatment of rosacea, eczema, or acne.

14. Does a small study without adverse effects prove full safety?

No. Small studies have limited ability to detect rare reactions, delayed hypersensitivity, or effects occurring in groups not included in the study. In the tetrapeptide-68 study involving 25 women for 12 weeks, no adverse reactions were reported. [16] The correct conclusion is therefore: no adverse reactions were reported under the conditions of this study, and not: the component is completely safe for everyone.

15. Does a home attempt to apply a cosmetic product on a small fragment of skin replace clinical flat-surface tests?

No. Home testing and clinical flat-plate testing address different questions. Professional flat-plate testing is used, among other things, to diagnose suspected allergic contact dermatitis using specific procedures and interpretation of the results. The FDA discusses professional testing in cases of suspected allergies to cosmetics.[2] Home testing does not rule out all delayed or cumulative reactions.

16. Does the appearance of irritation mean that the peptide is starting to work?

No. Irritation is not a confirmed marker of the effectiveness of a peptide. Itching, redness, irritation, or an increase in the severity of the changes can have many causes. The mere presence of a peptide does not mean that the discomfort is a beneficial „activation” of the skin. Effectiveness should be evaluated based on appropriate test results, not the occurrence of irritation.

17. What evidence is most useful in evaluating a peptide product for sensitive or acne-prone skin?

The most useful are the actual formulation studies conducted in a clearly defined, appropriate population, with a proper comparator and endpoints corresponding to the declared action. A controlled study under the background of people with sensitive skin and a multi-component anti-acne product address different questions. [3] [7] Hydration, barrier integrity, stinging, crusting, comedones, total number of lesions and disease severity should remain separate results.

18. Does „hypoallergenic” mean that a peptide product cannot cause allergies?

No. The term „hypoallergenic” should not be interpreted as a guarantee that no person will react to the product. Ready-made formulations contain many ingredients, and individual sensitivity varies. The FDA also warns against treating the term „hypoallergenic” as a federal guarantee in the United States.[2]

19. Can the product be non-comedogenic and at the same time irritate the skin?

Yes. Comedogenicity and irritation are different endpoints. The formulation may not increase the number of comedones under the tested conditions, yet in some people it can cause tingling, dryness, or other reactions. Similarly, a comfortable formulation was not automatically considered non-comedogenic.

20. Does improvement of the skin barrier indicate the treatment of rosacea or eczema?

No. Measurements related to the skin barrier provide useful information about the functioning of the skin, but treatment of the disease requires broader clinical results. In the BSFAB study, parameters related to the barrier were described in people who declared themselves to have sensitive skin.[3] This was not a study of the treatment of rosacea or atopic dermatitis.

21. Can a peptide inhibit Cutibacterium acnes in the laboratory but still not improve acne in humans?

Yes. Antimicrobial activity is only one element of the evidence chain. The peptide must also be stable, reach the appropriate environment, be well tolerated, and lead to a significant change in the clinical parameters of acne. The laboratory result alone does not confirm all of these stages.

22. Does the term „anti-inflammatory” mean a proven anti-inflammatory effect?

Not necessarily. „Soothing” may refer to a subjective reduction in discomfort or another cosmetic effect. Proofing the molecular anti-inflammatory action is a separate research question. A cosmetic product can improve skin comfort without showing a demonstrated inhibition of a specific inflammatory pathway in humans.

23. Does a randomized study show which component of the multivitamin serum worked?

Not necessarily. Randomization strengthens the comparison of interventions, but it does not isolate a single component if several elements differ between the formulations being tested simultaneously. The study of serum containing niacinamide, postbiotics, and peptides provides data on the entire tested combination, rather than evidence that the difference in hydration was due to the peptides themselves. [15]

24. Can the studies of naturally occurring human peptides be used as evidence of the efficacy of cosmetic peptides?

Only with great caution. Endogenous peptides such as CGRP or LL-37 are involved in human biology, but studies of these molecules do not automatically apply to other synthetic or cosmetic peptides.[10][11] Peptides differ in sequence, biological target, concentration, mode of delivery, and function.

25. Does a cosmetic product have to cure a disease in order to be useful for sensitive skin?

No. Cosmetics can provide significant benefits such as improved hydration, improved specific skin barrier parameters, greater comfort, or better tolerance without treating the underlying disease. The problem only arises when cosmetic results are extended to unproven claims regarding the treatment of acne, rosacea, eczema, or other diagnoses.

26. Does a positive opinion from one person prove that the peptide product is suitable for sensitive skin?

No. Individual experience describes a specific person’s reaction, but does not confirm overall tolerance. People differ in allergies, skin conditions, routine skincare, environmental exposure, and susceptibility to irritation. Opinions can be useful in assessing consistency or user experience, but claims about the entire population require research.

27. Does the appearance of new changes after starting to use a peptide product always mean „purging”?

No. The appearance of new changes should not be automatically considered as „purging”. Acne can naturally change in severity, and the new formulation may contain many ingredients that affect the skin. Irritation, occlusion, other products used, or independent changes can also be significant. The peptide itself does not mean that the initial deterioration is a necessary step before improvement occurs.

28. How best to interpret the statements regarding peptides in cosmetics?

First, it is necessary to determine exactly which peptide or formulation was tested, in which population, by what route the product was administered, what comparator was used, how long the study lasted and what result was measured. Then it is necessary to verify whether the declaration remains within these limits. The laboratory antibacterial activity should remain a laboratory result. The study of skin inflammation in mice should remain a preclinical evidence. The moisture content should remain a moisture-related result. The result regarding the multi-component product should remain a proof regarding that combination, unless the activity of the peptide itself has been isolated.

Limitations of the available evidence

The evidence regarding peptides used in the care of sensitive and acne-prone skin has several recurring limitations.

First of all, peptides are very chemically diverse.

The result for one peptide cannot be automatically assigned to another.

Secondly, the finished formulations are significantly different.

A peptide combined with niacinamide, acids, ingredients associated with retinoids or postbiotics is not the same as the same peptide placed in another matrix.

Thirdly, many studies analyze mechanisms, not clinical results.

Antimicrobial activity, receptor signaling, inflammatory markers, and animal studies can indicate interesting directions for further research, but they do not automatically confirm clinical efficacy.

Fourthly, the research populations are different.

Healthy volunteers, people with sensitive skin, people with acne, and patients with inflammatory skin conditions are not interchangeable groups.

Fifthly, the final scores also differ.

Moisture, barrier integrity, itching, comedones, crusts, growth of microorganisms and the exacerbation of the disease are all questions that are answered differently.

Sixthly, some of the studies include a small number of participants.

Small trials can provide useful preliminary results, but they have limited ability to detect rare reactions or confirm effects in a broad population.

Seventhly, multi-component products make it difficult to attribute the effect to a single component.

The improvement after the combination was used does not prove that the peptide was responsible for it.

After the eighth, some results are mixed.

In the study of granulysin-derived peptides, the number of crusts decreased, while the number of scaly patches increased.[6]

Such an outcome should not be reduced to a single positive statement.

Ninthly, negative results are also available.

The omignan study shows that the antimicrobial rationale did not translate into a clinically significant improvement compared to placebo in the disease studied [13].

Finally, a distinction must be made between cosmetic effects and the treatment of diseases.

The product can improve skin hydration or comfort without treating acne, rosacea, eczema, or any other recognized disease.

Summary

Peptides are increasingly appearing in cosmetics intended for sensitive and acne-prone skin. However, available studies do not justify treating „peptides” as a single, universally gentle, anti-inflammatory, non-comedogenic or therapeutic category of ingredients.

The evidence depends on the specific peptide, the specific formulation, the population being studied, and the measured outcome.

Some publications provide interesting data.

The BSFAB study described the results related to the skin barrier and the subjective assessment of skin condition in people who declared themselves to have sensitive skin.[3]

Results related to acne were obtained in a study of granulysin-derived peptides, but the changes in the individual types of skin lesions were mixed. [6]

Studies LZ1 showed antimicrobial and preclinical activity.[5]

Favorable results were also obtained for multi-component anti-acne and care products, but these studies do not allow the effect of the peptides themselves to be isolated. [7] [15]

Other data show that the biologically plausible mechanism should not be confused with clinical evidence.

Studies of naturally occurring peptides such as CGRP and LL-37 help to understand selected elements of skin biology, but do not confirm the action of non-related cosmetic peptides.[10][11]

Studies of skin inflammation in animals remain preclinical evidence. [12]

However, a controlled study of omignan shows that a peptide with a well-established antimicrobial mechanism may not bring the expected clinical improvement in a specific disease.[13]

The most reliable interpretation should therefore answer the following questions:

Which peptide?

What formulation?

What is the population?

What is the route of the exhibition?

Which comparator?

What is the endpoint?

How long has the study been conducted?

And what exactly was shown?

This approach allows for the reliable discussion of research on peptides in cosmetics without turning laboratory results into therapeutic claims and without assuming that a reassuring term on the label guarantees good tolerance.

Peptides are also studied in other areas of cosmetology, but evidence from one application should not be automatically transferred to others. For example, studies concerning hair cover other biological targets, models, and endpoints. More on this topic: Hair peptides: care, scalp products and scientific evidence.

Disclaimer

The article is purely educational and scientifically informative. It discusses cosmetic peptides, research on sensitive skin, research related to acne, laboratory experiments, animal models, formulation studies, and selected studies involving humans.

It does not constitute medical or dermatological advice and does not recommend any peptide, cosmetic, anti-acne product, moisturizing cream, serum, or treatment method.

Laboratory results regarding antimicrobial activity, animal experiments, studies of individuals with sensitive skin, and studies of multi-ingredient formulations should not be automatically interpreted as evidence of treatment for acne, rosacea, eczema, allergic contact dermatitis, or other recognized skin diseases.

Persistent, aggravated, painful, worsening, or otherwise distressing skin symptoms should be evaluated by an appropriately qualified specialist.

References

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