Signaling peptides in skin care: terminology and scientific evidence

Signaling peptides used in skincare are usually described as peptide ingredients that can influence cellular responses related to skin appearance and condition, extracellular matrix activity, or other biological processes relevant to cosmetic claims. However, the term „signaling peptide” describes the proposed function. It does not prove that every cosmetic containing such a peptide effectively releases it, delivers it to the appropriate site in the skin, triggers the intended cellular response, or provides a visible effect in humans.

An additional source of misunderstandings is the closely related term „signal peptide” used in molecular biology.

In molecular biology, a signaling peptide often means an amino acid sequence found in a newly synthesized protein that helps direct that protein through cellular transport and localization pathways. This intracellular process is scientifically different from applying a small cosmetic peptide to the surface of the skin.

Therefore, terminological similarity can lead to misleading combinations of research areas that actually address completely different questions.

Understanding this distinction greatly facilitates the interpretation of evidence. The identity of the component, the experimental mechanism, the stability of the formulation, skin exposure, cellular response, and clinical outcome are all interrelated, but they constitute separate issues. A credible declaration regarding a cosmetic product should combine these stages with appropriate evidence, rather than treating the term „signaling” itself as confirmation of the entire chain of events.

What do the statements regarding signaling peptides in cosmetics mean?

Functional description, not just a standardized component

In cosmetic terminology, the term „signaling” usually means that a given peptide has the ability to influence the behavior of cells.

Depending on the peptide and the research model, the proposed response may include the production of extracellular matrix components, the regulation of stress-related pathways, changes in cellular communication, or another biological process potentially related to skin appearance.

It is not necessary to treat all these potential effects as one mechanism.

Different peptide sequences can interact with different biological systems. Even peptides with similar structures can elicit different responses depending on the concentration, chemical modification, type of cells, exposure time, and experimental conditions.

Signaling peptides therefore do not constitute a single standardized pharmacological intervention.

More useful scientific questions are specific:

Which peptide was studied? In which model? At what concentration? What biological process was altered? How was this change measured?

The general statement that „peptides send signals to the skin” may be a useful simplification, but it does not answer the question of whether a specific peptide contained in a specific formulated product changes a specific parameter of human skin.

Example of KTTKS

One of the most frequently discussed examples is the Lys-Thr-Thr-Lys-Ser sequence, abbreviated KTTKS.

In an early primary study, this five-amino acid sequence was identified in the propeptide fragment of type I collagen and stimulation of collagen and fibronection production was noted in the investigated cultures of mesenchymal cells.[1]

This is an important mechanistic example, because the experiment used a precisely defined peptide sequence and measured specific biological results.

However, this was not a clinical study of a face cream, serum, foundation, or any other ready-made cosmetic product.

The experiment therefore does not prove that every peptide derived from collagen triggers the same response; that locally applied KTTKS automatically reaches the appropriate human skin cells; or that every cosmetic containing a related peptide visibly reduces wrinkles.

This distinction also helps to avoid the frequent terminological error.

KTTKS is a small peptide fragment associated with the precursor protein. It is not a complete collagen molecule.

If the sequence is modified chemically, for example by attaching a group derived from a lipid, the resulting molecule should be treated as a chemically different material, whose behavior in the formulation, stability, and distribution in the skin may differ from the properties of the original sequence.

Sequence and cellular context are important

Previous studies involving overlapping fragments of procollagen have shown that different fragments do not necessarily produce identical effects.

Some fragments stimulated the production of extracellular matrix components, while others did not, and the observed response also depended on the state of the cultured cells.[2]

The correct conclusion is therefore not simply to state that „collagen peptides work”.

These results rather show that biological activity may depend on the exact sequence and context of the experimental setup.

A positive result in one cell model and a negative result in another do not have to be contradictory. Both can help determine the conditions under which the proposed mechanism exists or does not exist.

Therefore, a broad functional category does not allow for reliably predicting every biological response.

The sequence, concentration, exposure time, cell type, culture conditions, and the specific endpoint measured constitute integral elements of the experimental result.

These details should remain visible even when the results of laboratory tests are presented to cosmetics consumers.

„Signage” does not automatically explain every step of the route

Observing a change in a specific cellular outcome does not mean that the entire molecular pathway responsible for that change has been identified.

The study may, for example, show increased production of a specific extracellular matrix protein without identifying the receptor that initiates the response or without proving all the intermediate signaling steps between exposure to the peptide and the measured result.

This distinction is important because simplified explanations sometimes transform the observed response into a supposedly fully understood mechanism.

Evidence regarding the mechanism becomes stronger when researchers test competing explanations and employ experimental controls capable of challenging the proposed pathway.

Depending on the question, this may include inactive comparative sequences, receptor blocking experiments or molecular targets, cell viability controls, concentration-response studies, measurements at different time points, or confirmation of the same biological change using more than one analytical method.

These are general principles of designing mechanistic studies.

This does not mean that every experiment involving cosmetic peptides has performed all of these tests.

A thorough review of the evidence should therefore distinguish what the researchers directly measured from what they inferred.

If the study merely proposes a specific pathway, rather than experimentally demonstrating all its stages, the mechanism should not be presented as fully confirmed in living human skin.

Signal peptides and signaling sequences that guide proteins

Protein targeting is an intracellular process

Cells produce proteins in the process of ribosomal translation.

Some newly-formed proteins contain sequences recognized by cellular mechanisms responsible for directing them to specific membranes or elements of the secretory pathway.

Structural studies of the signal-recognizing mammalian particle SRP (signal recognition particle) analyzed the way in which this mechanism recognizes the exposed sequence directed onto the resulting protein and then interacts with its receptor. [3]

In this scientific context, the word „signal” refers to information encoded in the protein sequence that helps the cell process and direct that protein.

This does not mean that a small peptide applied externally in a cosmetic product automatically instructs the skin cells to produce collagen.

Therefore, the terminological similarity should not obscure the difference between these processes.

Publications on molecular biology regarding the targeting of proteins cannot be used as evidence that a locally applied cosmetic peptide penetrates through the skin, reaches the skin's own cells, stimulates the production of extracellular matrix, or reduces wrinkles.

Similar terminology can hide different questions.

The term „signal peptide” is sometimes used in the cosmetic context for ingredients such as KTTKS derivatives.

In the literature of molecular biology, however, the same term can mean an amino acid sequence that directs the newly synthesized protein through intracellular transport pathways.

The correct meaning depends on the context.

The article based on evidence should indicate whether it discusses a free cosmetic peptide, a chemically modified local ingredient, a peptide fragment studied for its cellular activity, or a sequence within a larger, newly synthesized protein.

This distinction is particularly important when searching through databases of scientific publications.

Searches involving words such as „signal”, „peptide”, „skin”, „collagen” or „cell” may return studies on protein secretion, immunological signaling, disease pathways, antimicrobial peptides, intracellular transport and many other biological systems unrelated to the cosmetic ingredient under study.

The mere concordance of key words does not therefore confirm the scientific significance of a given publication.

This comparison shows why terminology alone cannot replace evidence.

Each of these categories answers a different question, so evidence belonging to one category cannot be automatically used to draw conclusions about another.

The sequences that direct proteins do not guarantee penetration through the skin

The protein-driving sequence fulfills its function in a specific intracellular biological environment.

This does not mean that a locally applied product using similar terminology can cross the skin's external barrier, remain intact, reach living cells, or, after external application, interact with the same molecular mechanism.

The skin exposure must be tested separately.

The formulation must first contain the intended molecular material in the appropriate form. The peptide must maintain sufficient stability during storage and use. It must then be released from the formulation, come into contact with the skin, and reach the site appropriate for the proposed mechanism.

Each of these stages may involve restrictions.

Therefore, the attractive schematic depicting the intracellular signaling pathway does not constitute evidence of the local delivery of the peptide.

Such a pattern can show what theoretically could happen after the molecule reaches its biological target.

However, it does not prove that the finished cosmetic product actually provides such exposure.

Categories can be superimposed, but they are not equivalent.

Peptides can be classified according to various properties.

One term may refer to the molecular origin, another to chemical modification, and a third to the proposed biological function.

For example, the terms „derived from collagen”, „palmitoylated” and „signal-mediated” do not have to be mutually exclusive.

One peptide may potentially fall into all three categories.

However, none of these labels independently confirms the full mechanism or the clinical outcome.

Similarly, not every cosmetic peptide is best classified as a signaling peptide.

Some may be used due to a different proposed function, while others may occur in complex mixtures in which the proportion of individual peptide components has not been experimentally isolated.

A useful classification should explain these differences.

It should not create hierarchies suggesting that one category is automatically more effective, more advanced, safer, or better documented than another.

Mechanistic studies and skin exposure

The experimental model sets the limits of the conclusions

Different experimental systems answer different scientific questions.

Cell culture allows the study of cellular responses during controlled, direct exposure.

Skin extracts and homogenates can help in analyzing degradation or molecular stability.

Models using cut-out skin can provide information about the distribution of the molecule in different layers of the skin.

Cosmetic studies involving humans assess the results obtained when a specific finished product is used under defined conditions.

These systems complement each other, but are not interchangeable.

Direct addition of the peptide to cultured cells bypasses the skin barrier and the release process of the component from the formulation.

Homogenized tissue no longer retains the full architecture of living skin.

The excised skin retains important structural features, but does not replicate all the physiological processes occurring in live human skin or all aspects of the normal use of the product.

Therefore, in mechanistic results, the model used must be clearly specified.

The result obtained in human fibroblasts in culture remains a laboratory cellular experiment.

The human origin of the cells does not change this experiment into a clinical trial demonstrating improvement in the appearance of the facial skin in humans.

Chemical modification can change the behavior of a peptide

Chemical modification can affect the physical and biological properties of a peptide.

Palmitoylation involves the addition of a group derived from a fatty acid to the peptide.

The resulting molecule is therefore chemically different from the unmodified sequence and may behave differently in terms of formulation, stability, phase separation, and distribution in the skin.

In studies comparing KTTKS and palmitoyl-KTTKS in hairless mouse skin and related skin preparations, differences were noted in the stability and recovery of both forms from the skin layers.[4]

In the experimental conditions used, none of the peptides were detected in the receiving solution after passage through the full thickness of the skin. [4]

These results justify treating modified and unmodified peptides as separate analytical materials.

They do not confirm identical behavior in human skin.

They also do not prove that palmitoilation provides a universal advantage in the delivery of any peptide, nor that the detection of a peptide in the skin layer automatically leads to a visible clinical effect.

Stability in the packaging and stability in the skin are different issues

The stability of a peptide is not a single universal property.

The peptide may remain chemically stable in the finished formulation during storage, but when applied to the skin it will find itself in a completely different environment.

Enzymes present in the skin, water content, pH, temperature, proteins, lipids and other local factors can influence the molecule's further fate.

On the other hand, the instability demonstrated under certain laboratory stress conditions does not mean that the product available for sale must degrade during normal storage.

In the KTTKS studies, skin extracts, homogenates, and permeation experiments were used to analyze various aspects of peptide behavior.[4]

These methods provide valuable data within the limits of the experimental conditions applied.

However, they should not be generalized automatically to every formulation or actual usage conditions.

A more comprehensive assessment of the formulation includes chemical identity, peptide content, formulation stability, release, and skin exposure.

Analytical studies of palmitoyl peptides in cosmetic preparations show that these materials can be measured using appropriate analytical techniques.[5]

However, confirmation of the presence of a component remains something other than demonstrating that it reaches the proposed site of action or produces a clinical effect.

Delivery is not a „all or nothing” category”

The term „penetration” can blur the important differences that occur in studies of the distribution of substances in the skin.

The peptide can remain mainly on the surface, enter the stratum corneum of the epidermis, reach deeper layers of the skin in the experimental model, or appear in the receptor chamber on the other side of the fully thick skin.

These are separate observations.

For example, in one experimental study of formulations containing acetylated hexapeptide, limited penetration to deeper layers was observed, while another study showed that the delivery of the peptide differed depending on the formulation carrier used.[6][7]

These studies provide useful examples of the relationship between delivery and formulation.

However, they should not be treated as identical experiments involving all cosmetic signaling peptides.

The biologically relevant location also depends on the proposed effect.

The moisturizing effect associated with the skin surface does not necessarily require the same molecular exposure as the claim regarding fibroblasts or other cells located deeper in the skin.

Researchers should therefore define what „delivery” or „absorption” means in a particular experiment, rather than treating these terms as uniform categories.

The evidence should combine the exposure with the proposed answer.

The convincing mechanistic argument requires determining whether the biological response occurs under exposure corresponding to the conditions of use of the finished cosmetic product.

A cellular experiment conducted at a specific laboratory concentration does not prove that the same concentration reaches the appropriate cells when the consumer applies serum or cream.

The difference can be significant, because cultured cells can be exposed directly, whereas topical use requires the release of the peptide from the formulation and its passage through or into the skin structures.

It is also necessary to distinguish between the intact peptide and its fragments, the total analytical signal from the measurement specific to the particular molecule, and changes in biological markers from the apparent clinical results.

These distinctions prevent the interpretation of analytical observations from extending beyond what the experiment allows.

No single test covers the entire chain of evidence.

The analysis of the formulation content, the stability experiment, the skin delivery study, the mechanistic cellular study, and the controlled clinical trial analyze the various elements of this chain.

Not every research program needs to include all of these elements.

However, if one of them is missing, the gap should remain visible, rather than being filled with an attractive narrative about „signaling”.

Evidence from cosmetic research in humans and its limitations

A controlled study of a moisturizing cream as a specific example

In a randomized, double-blind split-face study involving 93 women, a moisturizing cream containing palmitoylated pentapeptide was compared with a cream without the peptide for 12 weeks.[8]

Researchers noted an improvement in wrinkle-related ratings compared to the control formulation.[8]

The use of a matched baseline is important because it provides stronger information about the possible contribution of the component than an uncontrolled „before and after” comparison.

Nevertheless, the conclusion remains limited to the studied formulation, population, duration, comparator, and measured endpoints.

The study does not prove that every signaling peptide has the same effect.

It also does not show that the observed result persists indefinitely after cessation of use, nor that the proposed cellular mechanism occurred exactly according to the hypothesis in the skin of each participant.

The measured clinical effect regarding appearance and the direct confirmation of the underlying molecular mechanism remain separate conclusions.

Small studies require analysis that goes beyond abstract concepts

In a smaller randomized study involving 21 women, two peptide creams were compared with a placebo for eight weeks.[9]

The relatively small sample size and the exploratory nature of the study limit the possibility of generalizing the results to larger populations or using them to create a ranking of peptide formulations.

Small studies can lead to inaccurate estimates.

Different endpoints can also give different results.

For example, a favorable photographic assessment is not automatically equivalent to a statistically confirmed instrumental measurement.

Before considering one peptide or formulation to be superior, the full results, statistical analysis, the behavior of the comparator, cases of withdrawal and limitations of the study must be considered together.

Therefore, individual positive statements from the abstract should not replace the evaluation of the entire publication.

Abstracts are necessarily brief.

Full reports may include caveats, non-significant results, subgroup analyses, adverse effects, or methodological details that significantly influence interpretation.

Evidence regarding the entire formulation and the individual components should not be combined.

Many cosmetics contain numerous potentially active ingredients.

The finished cream may contain peptides along with humectants, emollients, lipids, antioxidants, plant ingredients, and other substances that can affect the appearance or hydration.

If the entire formulation improves a specific parameter, the individual contribution of each component may remain unknown.

A tailored formulation that does not contain the peptide can help investigate its role.

Comparing it with an entirely different moisturizing cream answers another question: which complete product worked better under the test conditions?

Studying the entire care routine introduces even more variables and may not allow the activity of a single product to be isolated.

The declaration should therefore be derived from the research project.

A favorable result regarding the entire routine should not be presented as evidence that the observed change was caused by the signaling peptide itself.

Similarly, the evidence regarding a single cream under review does not guarantee the effectiveness of any serum, mask, eye cream, foundation, or other cosmetic product containing the same peptide.

The endpoints and duration determine the scope of possible conclusions

Clinical results should be described precisely.

Assessment of wrinkles, standardized photography, imaging of the skin surface, measurements of skin moisture, mechanical properties of the skin, participant satisfaction, and the researcher’s assessment measure different aspects of the cosmetic product’s efficacy.

The study should therefore indicate what has changed, against what, to what extent and over what period.

An instrumental change does not necessarily mean that participants or observers will notice a noticeable difference.

Similarly, the participants' satisfaction can provide valuable information, but it does not confirm a specific molecular mechanism occurring in the tissue.

Both types of information can help in evaluating the product if their significance is clearly defined.

The duration of the study is also important.

A few weeks of regular use can show what happened during that period.

This does not automatically indicate a lasting reconstruction of the skin.

Statements regarding the maintenance of the effect after discontinuation of use require further monitoring after discontinuation of the product.

Similarly, the results obtained in the selected group of participants should not be automatically generalized to all age groups, skin types, ethnic origins, or clinical conditions.

The safety and quality of the evidence remain product-specific.

A biologically plausible peptide component is not automatically harmless in every formulation or suitable for every user.

Tolerance depends on the entire formulation, concentration, method of exposure, other ingredients, and the individual characteristics of the user.

Clinical reports should therefore describe adverse reactions, irritations, cases of discontinuation, and relevant exclusion criteria together with beneficial efficacy results.

The quality of the evidence also depends on the research design.

The sample size, randomization, blinding, choice of comparator, pre-defined endpoints, transparent statistical analysis, completeness of reporting, and independent replication of results all influence the level of certainty.

Commercial relationships and sources of funding should also be disclosed.

The involvement of industry does not automatically invalidate the research, just as independent funding does not automatically guarantee high-quality methodological methods.

The funding should be evaluated together with the project and the way the research is reported on.

The most useful conclusion remains therefore precise:

Some precisely defined peptide formulations have evidence from human cosmetic studies, whereas the broad term „signaling peptides” can go far beyond what has actually been demonstrated.

Understanding the term „signaling peptide” should help to formulate the scientific question precisely, rather than replacing the answer to that question.

Frequently asked questions

1. Are cosmetic signaling peptides the same as signaling peptides in molecular biology?

Not necessarily. The terminology may overlap in cosmetic texts, but in different fields of science these terms often describe completely different phenomena. In cosmetology, signal peptides usually denote peptide components that are believed to influence cellular responses. In molecular biology, signal sequences guiding proteins are fragments of newly synthesized proteins involved in their intracellular transport and direction. Structural studies of the signal-recognizing molecule deal with the latter process specifically.[3] The context is therefore crucial. Evidence regarding the intracellular transport of proteins cannot directly confirm the action of a topical cosmetic because in both cases the word „signal” is used.

2. Does the cellular signaling result confirm the anti-wrinkle effect?

No. The cellular response does not prove that the finished cosmetic product effectively releases the peptide, delivers sufficient amounts of intact material to the appropriate site in the skin, or changes the appearance of wrinkles in humans. KTTKS studies concerned the production of extracellular matrix associated with cultured cells. [1] This is mechanistic evidence, not a clinical study of wrinkles. The wrinkle claim requires appropriate human study using the actual formulation and a proper endpoint.

3. What does KTTKS mean?

KTTKS is a one-letter abbreviation for the five-amino acid sequence lysine–tryptophan–tryptophan–lysine–serine. This sequence was identified in the propeptide fragment of type I collagen and its biological activity in cell cultures was studied. [1] Knowledge of the sequence allows determining the chemical identity of the material in question, but it does not provide universal cosmetic efficacy. Modified forms, different concentrations, and ready formulations raise additional questions regarding stability, delivery, exposure, and clinical activity.

4. Is palmitoyl-KTTKS identical to KTTKS?

No. Palmitoyl-KTTKS contains a chemical modification that makes it a different molecular material than unmodified KTTKS. Comparative studies in skin models showed differences in the stability and recovery of both forms from the skin layers. [4] These results justify their differentiation rather than the use of interchangeable names. However, they do not confirm identical behavior in human skin or in every cosmetic formulation.

5. Are all signaling peptides fragments of collagen?

No. The term „signaling” describes the proposed biological function, not a single universal molecular origin. KTTKS is a well-known example associated with collagen, but the results regarding KTTKS do not define all the peptides sold as signaling peptides. [1] Other peptides may have different sequences, origins, modifications, molecular targets, and proposed effects.

6. Does a peptide need to get into the bloodstream to affect the skin?

Not necessarily. The proposed local action in the skin and systemic exposure are separate scientific questions. Theoretically, the peptide can interact with the appropriate area of the skin without achieving a measurable concentration in the circulation. In experimental studies, peptide material was detected in skin layers without its detection in the receiving chamber on the opposite side of the full-thickness skin. [4] This does not confirm clinical efficacy, but it shows why systemic exposure is not the only relevant endpoint regarding delivery.

7. Does palmitoilation guarantee penetration through the skin?

No. Palmitoylization changes molecular properties, but such chemical modification does not guarantee delivery from every formulation or penetration into every layer of the skin. Comparative laboratory results for palmitoyl-KTTKS depend on the specific experimental model, vehicle, analytical method, and study conditions. [4] The declaration regarding delivery from the finished product therefore requires evidence relating to that specific formulation. Designing a molecule for delivery and experimentally demonstrating delivery are not the same thing.

8. Does every peptide associated with collagen stimulate the same response?

No. Experiments with different fragments of procollagen showed differences in biological activity, and the state of the cultured cells also influenced the response. [2] Therefore, common origin does not make peptide fragments biologically equivalent. The results specific to the sequence and model should remain related to the material that was actually studied.

9. Does the increase in gene expression mean a greater amount of functional protein?

No. mRNA expression, protein production, its modifications, tissue organization, and the visible clinical effects are different biological levels. A change at one level does not automatically confirm the others. Previous studies of procollagen fragments even showed changes in proteins without corresponding measurable changes in the analyzed mRNA level.[2] Therefore, the results regarding gene expression should not be extended to the immense remodeling of tissue or the visible cosmetic effect.

10. Can the protein-driving sequence bypass the skin barrier?

This cannot be inferred from its intracellular function. Signal-sensing molecule research concerns the recognition of newly formed protein sequences during the process of directing proteins within the cell.[3] It does not prove that an externally applied cosmetic ingredient exceeds the intact skin barrier. Delivery to the skin remains a separate experimental question involving formulation release, molecule stability, skin interactions, and distribution.

11. Does the laboratory concentration correspond to the exposure obtained from the serum?

No. Cultured cells can be directly exposed to a precisely defined concentration of the peptide, bypassing both formulation release and passage through the skin barrier. Locally applied serum introduces several additional steps before the peptide could reach the same cells. Formulation studies show that delivery can vary depending on the properties of the carrier. [7] Therefore, laboratory concentrations cannot simply be equated with the amount reaching target cells during normal cosmetic use.

12. Do all peptide signaling creams have proven clinical efficacy?

No. Evidence from human studies refers to a specific intervention that was actually tested. A controlled study of a moisturizing cream containing palmitoylated pentapeptide may justify conclusions regarding the formulation, population, duration, comparator, and measured results [8]. It does not automatically confirm the efficacy of other creams containing different concentrations of the peptide, derivatives, carriers, or additional ingredients.

13. Does the improvement in hydration confirm the signaling mechanism?

No. Hydration is a product-wide outcome and may depend on many formulation elements, including humectants, emollients, occlusive agents, film-forming ingredients, and the entire carrier. Demonstrating greater hydration does not identify the receptor, intracellular pathway, or specific peptide contribution on its own. Mechanistic studies and studies regarding the attribution of the effect to a specific component require appropriate experimental designs.

14. Does „more powerful signaling” have to mean a better effect?

No. The term „more robust signaling” does not describe a standardized clinical outcome, and a greater laboratory response does not necessarily mean a more favorable outcome. Biological signaling depends on the context, and the relationship between the magnitude of the response and the apparent cosmetic effect may not be linear. Fragment studies show that activity can vary depending on the experimental system. [2] Therefore, a clinically relevant statement must refer to the appropriate outcome.

15. Are favorable photos more important than the lack of an effect in instrumental measurements?

Not automatically. Photography and instrumental measurements can assess different characteristics, and the photos may depend on lighting, settings, facial expressions, camera parameters, and the way they are evaluated. Therefore, a small cosmetic examination should be interpreted based on the full set of results, not just the most favorable one. [9] If individual endpoints yield different results, the discrepancy itself is important scientific information and should be presented.

16. Are signal peptides automatically non-irritating?

No. The proposed signaling function does not guarantee universal tolerance. Safety depends on the entire formulation, concentration, method of exposure, other ingredients, and the characteristics of the person using the product. Small clinical studies cannot also rule out any rare adverse effects. Safety reporting should therefore include irritations, adverse reactions, withdrawal cases, and significant characteristics of the participants.

17. What evidence makes the declaration regarding the signaling peptide convincing?

A convincing declaration identifies the exact peptide, demonstrates a reproducible response in the appropriate experimental model, provides evidence that the formulated product can provide reliable exposure at the appropriate site on the skin, and assesses the intended outcome in humans using a suitable comparator. A single experiment does not have to answer all questions, but the relationships between the individual levels of evidence should be clearly presented. Controlled studies of moisturizing creams constitute an example of a clinical component of such a chain of evidence. [8] Unresolved issues should remain clearly marked, rather than being filled with mere terminology.

Summary

Signal peptides used in skincare and signal sequences directed by proteins belong to different scientific contexts, although they are sometimes described using similar terminology.

In cosmetic research, the term „signaling peptide” usually describes a proposed function: it is assumed or demonstrated under specific experimental conditions that a specific peptide influences a cellular response essential for biology or the appearance of the skin.

In molecular biology, a signaling peptide or a guiding sequence can, however, represent the information contained in the newly synthesized protein and involved in its intracellular transport.

Confusing these concepts can make the evidence appear stronger or more directly related to local skin care than it actually is.

Mechanistic studies using precisely defined peptides such as KTTKS show why sequence and experimental context matter. Some peptide fragments can alter the measured cellular responses under specific laboratory conditions, while related fragments may behave differently. Chemical modifications can further alter stability and distribution.

However, the mechanistic response does not automatically confirm the delivery of the peptide during topical use.

Similarly, demonstrating delivery does not automatically mean a visible clinical benefit.

The most informative evidence therefore combines several separate questions: what molecule is present in the product, whether it remains stable, whether the formulation releases it, where in the skin it reaches, what biological response occurs under appropriate exposure, and whether the finished product produces the claimed effect in humans.

Cosmetic evidence involving humans is most powerful when a precisely characterized finished formulation is compared with a corresponding control, and the study clearly presents individual results instead of combining instrumental measurements, participant perceptions, mechanistic assumptions, and clinical changes in appearance into a single broad statement.

Some precisely defined peptide formulations have evidence from cosmetic studies in humans.

However, this does not mean that everything that is sold as a signaling peptide acts in a universal way.

The term „signal” should therefore lead to a precise scientific question, and not serve as evidence of effectiveness.

Disclaimer

This article is for educational and scientific informational purposes only. It explains the terminology related to cosmetic signaling peptides, signaling sequences in molecular biology, experimental models, skin delivery studies, formulation science, and the interpretation of cosmetic evidence. It does not recommend a product for skin care, does not recommend treatment, does not diagnose skin diseases, nor provides individual dermatological advice.

Laboratory results obtained using cultured cells, skin extracts, homogenates, excised skin, animal models, or isolated peptide components should not be automatically interpreted as evidence that the finished product used topically produces the same effect in humans.

Similarly, evidence regarding a single peptide sequence, a chemical derivative, concentration, formulation, moisturizing cream, serum, or clinical population does not confirm the efficacy, safety, delivery, or usefulness of another product.

The reliability of the mechanism, the presence of the peptide, the stability of the formulation, skin exposure, cellular response, and the apparent clinical benefit are separate evidence questions. A positive result at one stage does not automatically confirm subsequent results.

Individual tolerance may also vary depending on the formulation and the person using the product. In case of persistent irritation or a dermatological disease, individual advice from a suitably qualified physician or dermatologist should be sought.

References

1. Katayama, K., Armendariz-Borunda, J., Raghow, R., Kang, A. H., & Seyer, J. M. (1993). A pentapeptide from type I procollagen promotes extracellular matrix production. Journal of Biological Chemistry, 268(14), 9941–9944. https://pubmed.ncbi.nlm.nih.gov/8486721/
2. Katayama, K., Seyer, J. M., Raghow, R., & Kang, A. H. (1991). Regulation of extracellular matrix production by chemically synthesized subfragments of type I collagen carboxy propeptide. Biochemistry, 30(29), 7097–7104. https://doi.org/10.1021/bi00243a009
3. Jomaa, A., Eitzinger, S., Zhu, Z., Chandrasekar, S., Kobayashi, K., Shan, S. O., & Ban, N. (2021). Molecular mechanism of cargo recognition and handover by the mammalian signal recognition particle. Cell Reports, 36(2), Article 109350. https://doi.org/10.1016/j.celrep.2021.109350
4. Choi, Y. L., Park, E. J., Kim, E., Na, D. H., & Shin, Y. H. (2014). Dermal Stability and In Vitro Skin Permeation of Collagen Pentapeptides (KTTKS and palmitoyl-KTTKS). Biomolecules & Therapeutics, 22(4), 321–327. https://doi.org/10.4062/biomolther.2014.053
5. 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
6. Kraeling, M. E., Zhou, W., Wang, P., & Ogunsola, O. A. (2015). In vitro skin penetration of acetyl hexapeptide-8 from a cosmetic formulation. Cutaneous and Ocular Toxicology, 34(1), 46–52. https://doi.org/10.3109/15569527.2014.894521
7. Hoppel, M., Reznicek, G., Kählig, H., Kotisch, H., Resch, G. P., & Valenta, C. (2015). Topical delivery of acetyl hexapeptide-8 from different emulsions: Influence of emulsion composition and internal structure. European Journal of Pharmaceutical Sciences, 68, 27–35. https://doi.org/10.1016/j.ejps.2014.12.006
8. 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
9. Aruan, R. R., Hutabarat, H., Widodo, A. A., Firdiyono, M. T. C. C., Wirawanty, C., & Fransiska, L. (2023). Double-blind, Randomized Trial on the Effectiveness of Acetylhexapeptide-3 Cream and Palmitoyl Pentapeptide-4 Cream for Crow’s Feet. Journal of Clinical and Aesthetic Dermatology, 16(2), 37–43. https://pubmed.ncbi.nlm.nih.gov/36909866/