„Repair of peptide bonds” is a much more precise statement than the claim that a given product smooths hair, makes combing easier, strengthens it, or reduces its brittleness. Peptide bonding is a specific type of covalent bond that links the remaining amino acids in a protein chain. Demonstrating that a product improves the appearance or mechanical properties of damaged hair fiber does not automatically mean that it reproduces the broken peptide bonds in the original keratin scaffold.
Hair products containing peptides have been studied in laboratory conditions, and some of the tested materials improved certain mechanical properties under specific experimental conditions. However, individual studies differ in terms of the peptides used, protein hydrolysates, formulations, models of hair damage, procedures, and proposed mechanisms of action.
A positive result for a specific peptide, hydrolyzed keratin product, or enzyme-containing system cannot therefore automatically confirm the effectiveness of any commercial product labeled as bond builder, a peptide treatment that regenerates the hair, or a „repairing peptide bonds” formula”.
The most useful way to assess such declarations is to separate the intended effect from the proposed mechanism.
What exactly changed after using the product?
How was this change measured?
What material was tested?
With what did the result be compared?
How long did the effect last?
And above all: has the proposed molecular mechanism been demonstrated independently, or was it merely inferred based on an improvement in hair properties?
In this article, we look at these differences without dealing with marketing terminology, ingredient names, or broad terms such as „repair” or „rebuilding connections” as proof in itself.
The construction of the hair fiber and terminology regarding the bonds
Wood is a complex structural material
The visible hair shaft consists primarily of keratinized material organized into several structural levels.
Exterior hair sheath (cuticle) It is largely responsible for surface properties, including friction, smoothness, and the way the hair interacts with cosmetic products. Located under it the hair core (cortex) it plays, however, an important role in its mechanical properties.
Damage occurring mainly on the surface can therefore cause different consequences than damage to deeper structural elements.
The product can also improve the condition of one area or one property of the hair without restoring all the characteristics of the original fiber.
In one study concerning the mechanics of human hair, the hierarchical structure of the hair and its response to factors such as deformation rate, humidity and temperature. The researchers demonstrated that the results of tensile strength measurements depend on experimental conditions and linked the observed reactions with structural changes related to keratin.[1]
This is of great importance when interpreting the claims regarding „stronger hair”.
The value describing strength is not a constant, universal characteristic of every hair. The result depends partly on what exactly is measured and under what conditions.
The humidity can affect the hair mechanics. The fiber’s elongation rate, its geometry, the previous history of treatments, and other elements of the experimental procedure also play a role.
Therefore, the results of mechanical testing must always be interpreted together with the method used to obtain them.
The visible hair shaft also differs biologically from living skin.
It does not regenerate using cellular repair mechanisms characteristic of living tissues.
However, this does not mean that cosmetic products cannot improve the properties of the hair.
The preparation can alter surface properties, reduce friction, affect interactions with water, deposit material in damaged areas, penetrate into accessible parts of the fiber, or increase its resistance to mechanical loads.
The most important question, therefore, is not whether hair can be „repaired” in any sense.
It is crucial to determine, what kind of repair was actually performed.
Peptide bonds form the protein skeleton
Peptide bonds connect the successive amino acid residues in the polypeptide chains that form the keratin proteins.
These covalent binding structures of the protein skeleton differ chemically from many other interactions involved in the formation of the hair structure.
This distinction is of fundamental importance for the interpretation of the term. „repair of peptide bonds”.
The damage to the polypeptide backbone is not chemically the same as the breaking of the hydrogen bond, the change in ionic interaction, the modification of the disaccharide bridge, or the disruption of the way neighboring protein structures interact.
Adding peptides to a formulation means introducing additional chains of amino acids or material containing peptides.
The mere presence of peptides does not, however, prove that they are covalently incorporated into the interrupted fragments of the original keratin skeleton.
There are many other mechanisms possible.
The peptide material can adsorb onto the surface of the fiber, form a layer or film, penetrate into accessible areas, interact electrostatically with damaged sites, form hydrogen bonds, participate in other noncovalent interactions, or — depending on the formulation — take part in cross-linking reactions.
These mechanisms can still lead to a significant improvement in the cosmetic or mechanical properties of the hair.
The product does not have to replicate the original keratin sequence to reduce friction, improve performance properties or increase the hair's resistance to breakage.
The scientific problem therefore primarily concerns precision of declarations.
The proposed mechanism should correspond to what the experiments actually showed.
More information about the peptides themselves, their structure and biology is worth considering separately from the claims regarding hair products. Similarly propeptides They refer to a specific biological issue and are not synonymous with peptides used in cosmetic hair formulations.
Not all connections should be treated as the same type.
There are several chemically and physically different types of bonds and interactions in hair. Simply calling them all „hair bonds” can hide important differences.
| Binding or interaction | General role in hair proteins | Importance for the declaration |
|---|---|---|
| Peptide bond | It combines the remaining amino acids in the polypeptide backbone | Recreating the original skeleton requires specific chemical evidence |
| Disaccharide binding | Kovalent bond involving sulfur groups derived from cysteine | It is a different chemical target than the peptide skeleton |
| Hydrogen bonding | It helps stabilize the structure of the protein and its interaction with water | Changes can affect the properties of the hair without re-bonding the skeleton |
| Ionic interaction | Attraction between charged groups | It depends on the local chemical environment |
| Hydrophobic and other non-covalent interactions | They participate in the organization of proteins and the properties of the material | Stronger binding does not automatically mean the creation of a new covalent bond |
| Embedded film or coating | It changes the fiber surface, friction and potentially water exchange | It can improve the properties without restoring the original protein sequence |
Definition „reconnection” therefore does not inform which of these mechanisms actually takes place..
This is important because evidence supporting one mechanism does not automatically support another.
For example, the improvement in non-covalent interactions with keratin is not evidence of the formation of new peptide bonds.
Similarly, the data regarding the chemistry of disaccharide bridges do not themselves indicate the reconstruction of a polypeptide backbone.
The history of damage changes the research question
Not all damaged hair is the same experimental material.
Shining, chemical straightening, repeated washing, ultraviolet radiation, thermal styling, environmental factors, and mechanical combing can all change hair in different ways.
As a result, the fibers may differ in surface state, protein structure, porosity, water behavior, and mechanical properties.
A product that is effective in one model of damage does not necessarily have to behave identically in another.
The origin of the hair, its structure, previous cosmetic treatments, environmental exposure, and the initial condition can also be important factors.
Research concerning Hydrolyzed keratin for example, it was carried out on chemically straightened hair with a specific structure.[2]
This is specific experimental material with a specific history of treatments.
The results may be useful for formulating hypotheses regarding other types of damaged hair, but they should not be automatically considered equivalent evidence for hair that has been bleached, has not undergone treatments, is thermally damaged, or any other type of damaged hair.
The same principle applies to the product format.
The rinse-off conditioner and the non-rinse-off product can contain a similarly named peptide ingredient, but provide completely different exposure conditions.
The contact time, the deposition of the component, the drying of the product, the amount of substance remaining on the hair, and the effect of subsequent washing can vary.
Therefore, the evidence should refer to both the material under investigation, as well as the conditions of use under investigation.
What exactly do the „repair” studies measure?
Appearance is one of the effects, not a test of the molecular mechanism
Gloss, smoothness, softness, reduction of puffiness, easier styling and the impression of greater volume can be significant cosmetic effects.
They describe the appearance, feel or behavior of the hair.
However, they do not in themselves indicate which molecular bonds have changed.
A smoother surface, for example, may result from the deposition of a conditioning substance or a reduction in friction.
The impression of greater volume may be related to a change in the fiber structure, the way the hair is arranged, a reduction in brittleness, or less tangling of the hair.
Various mechanisms can therefore lead to similar changes visible in the „before and after” photos.
Photographs can document the appearance.
However, they cannot independently demonstrate the reconstruction of peptide bonds within the keratin.
This does not mean that cosmetic effects on appearance are scientifically irrelevant.
It simply means that The appearance declaration and the molecular mechanism declaration require other types of evidence..
The tensile strength tests answer specific questions
In the stretching test, a single fiber is stretched under controlled conditions.
Depending on the protocol, it is possible to analyze the force required to break the hair, the degree of its elongation, the reaction to deformation, and other mechanical parameters.
These results are valuable, but the individual parameters are not interchangeable.
Strength when breaking it is not, for example, the same as stress at rupture.
The stress takes into account the cross-sectional area of the sample.
Similarly, stiffness is not the same as strength, flexibility, fatigue resistance, or resistance to repeated combing.
Therefore, the declaration of type „the hair became 30% stronger” it is incomplete without information about what exactly the word „stronger” means.
Was the tensile strength measured?
Tension?
Stiffness?
Extension?
Resistance to cracking?
Is there another parameter?
Only knowledge of the method, the conditions and the reference point allows one to properly interpret such a percentage.
The fragility tests answer another question
Controlled combing tests and other repeatable mechanical loads can assess the hair's resistance to breakage associated with grooming.
However, they answer a different question than the single fiber stretching test.
Both methods can be useful.
However, their results should not be treated as numerically equivalent.
In one of the more recent studies of designed peptides, computer analysis was combined with strength measurements, fracture tests, microscopy, and penetration assessment. The researchers described favorable results for specific tripeptides.[3]
The use of several complementary methods allows to assess various aspects of the material's behavior.
However, the results remain valid for specific peptides, formulations, the hair being studied, and the experimental conditions.
What would be needed to demonstrate the restoration of peptide bonds?
A convincing claim regarding the reconstruction of a peptide backbone would require more than just demonstrating that the fiber became mechanically stronger after the product was applied.
First, the initial chemical damage would have to be determined, and then it would have to be demonstrated that the product used restored the proper integrity of the skeleton.
The improvement in mechanical properties alone does not allow this to be stated, because the strength of the hair can be increased through many physical and chemical processes.
The deposition of material on the surface can alter the mechanical properties.
Penetrating substances can affect the effects in damaged areas.
Non-competitive effects can stabilize the structure.
Reinforcement can increase resistance to deformation.
None of these mechanisms need to involve the reconstruction of the original polypeptide sequence of keratin.
Spectroscopic methods can provide important chemical information, but they also require careful interpretation.
The peptide material itself contains amide bonds.
Therefore, the increase in the spectroscopic signal associated with amide groups after the use of the product may result, among other things, from the presence of bound peptide material, the formation of new network bonds, or other structural changes.
It does not automatically prove that the interrupted binding of the native keratin skeleton was re-connected in its original configuration.
The durability of the effect requires testing after subsequent washes.
The improvement observed immediately after using the product does not indicate how long the effect will last.
Further washing, brushing, styling, changes in humidity, the effect of temperature and the use of other products can affect both the deposited material and the mechanical properties of the hair.
Therefore, the durability declaration should specify which test was used and how many cycles were evaluated.
In the study of a system using keratin and an enzyme, measurable effects remained visible after five cycles of washing. [4]
This supports the conclusion that the effect will persist under the specific research procedure.
However, it does not prove a lasting reconstruction.
It also does not mean resistance to an unlimited number of shampoos, other styling products, repeated thermal styling, or all real grooming regimens.
The durability of the effect and the mechanism of its formation are separate questions.
Formulations containing peptides and product-dependent mechanisms
Hydrolyzed keratin is not one single peptide
Hydrolyzed keratin usually means a mixture or breakdown of fragments derived from protein, rather than a single precisely defined peptide with a specific sequence.
Individual preparations of hydrolyzed keratin can differ in their molecular mass distribution, amino acid composition, charge, processing method, and other physicochemical properties.
These differences can affect the way the material interacts with the hair.
In a study comparing hydrolyzed keratin fractions derived from wool with differing molecular masses, different patterns of surface adsorption and fiber penetration were observed. The individual fractions also influenced mechanical properties despite differences in the location of their interaction with the wool. [2]
These results undermine the too simplistic assumption that „smaller always means better”.
A smaller fraction can more easily reach certain areas of the damaged fiber.
A larger fraction that remains mainly on the surface, however, can still play an important role by forming a coating, film, or other effects.
Which property is more advantageous depends on the effect being studied.
Defined peptides can interact with hair in different ways
More precisely defined peptide materials derived from keratin were also studied.
A 2012 study evaluated a peptide derived from keratin in a water-based formulation and a formulation using an organic solvent on chemically straightened hair. Both formulations improved the selected measured properties, but differences were observed between the carriers used. [5]
This shows two important issues.
First of all, the same peptide can behave differently depending on the formulation.
The carrier can influence the delivery of the component, its attachment, interaction with the fiber, and the final properties of the material.
Secondly, a better result in a specific mechanical experiment does not automatically mean that a given formulation is more advantageous in all aspects related to safety or tolerance.
Non-competitive effects may support improved endurance
In a more recent study concerning designed tripeptides, they were evaluated KCV, also known as Tripeptide-132, and its palmitoyl derivative. [3]
Computer analysis suggested numerous interactions with keratin, in which hydrogen bonds played an important role. Experimental studies included, among other things, fiber strengthening, brittleness, microscopy, and penetration.
These results show an important distinction.
The component can be a peptide and can significantly interact with the hair keratin without forming new peptide bonds that connect the broken ends of the primary keratin skeleton.
„Peptide-containing” and „peptidic binding reconstruction” are therefore two different concepts.
Non-covalent interactions can still improve the material's properties.
The fact that the proposed mechanism is non-qualitative does not make the observed mechanical effect insignificant.
It merely changes the way in which this mechanism should be described.
Systems containing enzymes require separate evaluation
Formulations containing transglutaminase they use a more specific chemical approach related to networking.
In a 2023 study, a system containing keratin, serine, and transglutaminase improved several laboratory parameters.[4]
However, the presence of active enzyme makes this intervention significantly different from ordinary care using hydrolyzed proteins or peptides.
Therefore, the same mechanism cannot be applied to another product just because terms appear on its label. Keratin, peptides, protein regeneration or bond reconstruction.
The intervention is the entire system.
Preventing damage is not the same as reversing it
It is also important to distinguish between prevention of damage and reversal of already existing damage.
A 2025 study on hydrolyzed keratin and exposure to ultraviolet radiation described the deposition of material, partial penetration, and the preservation of tensile properties under specific experimental conditions.[6]
This study is relevant to the issue of resistance to a specific damaging factor.
However, it does not prove that the previously existing damage to the peptide skeleton has been reversed.
Therefore, it is necessary to separate three different results:
preventing deterioration of properties, improving the functioning of an already damaged fiber and recreation of the original molecular continuity.
Fragility and conditioning effects
Less fragility may be significant without indicating the growth of new hair
A product that reduces brittleness under the right conditions can help maintain the length of the hair and contribute to its fuller and healthier appearance.
This can be a significant cosmetic effect.
However, this is still the case effect regarding the hair fiber.
It does not demonstrate an increase in hair follicle activity, stimulation of new hair growth, or treatment of hair loss-related disorders.
This distinction is particularly important in the case of photographs showing an apparently greater density of the hairstyle.
Reducing brittleness can help maintain existing hair length.
Changes in styling, fiber diameter, surface properties, and the way the hair is tangled or crimped can also change the impression of its density.
None of these effects automatically mean that more follicles have entered the growth phase or started producing new hair.
Research on hair growth therefore requires methods designed specifically for assessing growth. This topic has been discussed separately in the article. peptides for hair loss.
Similarly, the effectiveness of a cosmetic cleansing product should be evaluated in the context of its specific formulation and the short time it is in contact with the hair and scalp. More about this: shampoo with peptides.
The type of comparison determines what can be attributed to the peptide
The control group used in the study has a significant impact on the conclusions that can be drawn.
A comparison of the hair subjected to the product with the hair not subjected to any treatment can show whether the complete formulation caused the difference.
However, he does not have to indicate which component was responsible for it.
Comparison with a formulation that is appropriately matched to the substrate It is more informative if the goal is to highlight the contribution of a peptide or other active component.
Hair products often contain many substances that can affect friction, smoothness, setting, conditioning, water resistance, and brittleness.
If several ingredients change simultaneously, a favorable result may well confirm the effectiveness of the complete formulation, but it leaves uncertainty regarding the contribution of the individual ingredients.
This does not mean that the product did not work.
It merely means that the evidence is more strongly supportive the effect of the finished product rather than the mechanism attributed to a single component.
Hundreds of fibers do not mean hundreds of independent participants
In material studies, a very large number of individual hair fibers can be analyzed.
However, these fibers can come from a small number of donors or from several strands of hair.
This difference has statistical and biological significance.
Examining 500 individual fibers is not equivalent to a clinical trial involving 500 independent individuals.
Hair from the same donor may have common characteristics related to genetics, structure, history of cosmetic procedures, environmental exposure, and baseline condition.
A large number of measurements can improve the precision of the characteristics of a particular sample of material.
However, it does not automatically prove that the result will be the same for different hair types, history of damage, climates, grooming methods, or user population.
How to properly read the „bond repair” declaration?
The information declaration regarding the restoration of connections should indicate the product under investigation, the model of the damage, the endpoint, comparison, proposed mechanism and durability of the effect.
It is best if it clearly specifies whether the evidence concerns surface attachment, fiber penetration, noncovalent interactions, covalent network formation, or the direct reconstruction of the damaged protein skeleton.
A general statement that the product simply „rehabilitates the ligaments”, It leaves all these questions unanswered.
A significantly narrower claim — for example, improved combing, greater resistance to breakage or improved mechanical properties — can, however, be very valuable if it is supported by a properly designed study.
A product does not become scientifically less convincing just because the declaration is more precise.
Quite the opposite: The strongest scientifically formulated statement is usually the one that most accurately corresponds to what was actually measured..
Frequently asked questions
1. Do smoother hair indicate repair of peptide bonds?
No. Smoothness is primarily a property related to appearance, feel, and the surface of the hair, rather than a direct measurement of the continuity of the keratinic protein structure. Coating, reducing friction, depositing ingredients, or changes in the behavior of the hair coat can cause the hair to become smoother without reconstructing the broken peptide bonds. If the experiment shows an improvement in smoothness, the most precise conclusion is an improvement in smoothness, unless the bond reconstruction has been demonstrated by independent chemical methods.
2. Can all „bond repair” products be treated the same way?
No. Products labeled as bond-rebuilding agents can vary significantly in chemical composition, formulation, proposed target, and evidence. The hydrolyzed keratin preparation, a tripeptide and an enzymatic system that causes cross-linking are different interventions.[2][3][4] Results regarding one system do not automatically confirm the action of another.
3. Is peptide binding the same as disulfide binding?
No. Peptide binding links the remaining amino acid residues in the polypeptide backbone, whereas disulfide bonding is a covalent bond involving sulfur-containing groups derived from cysteine. Both types of bonds are important for protein structure, but they are chemically different. Evidence of a product's effect on one type of bond does not automatically prove its effect on another.
4. Does adding peptides automatically re-link the keratin chains?
No. The peptides present in the formulation can interact with the hair without covalently binding to the interrupted native keratin chains. They can adsorb onto the surface, penetrate accessible areas, form a film, or participate in hydrogen bonding and other non-covalent interactions. The presence of the peptide itself does not necessarily indicate the reconstruction of the native keratin skeleton.
5. Can a dead hair be „repaired”?
The material properties of dead hair can be improved, but the hair shaft does not regenerate through the cellular processes characteristic of living tissues. Cosmetic products can affect surface properties, friction, interactions with water, elasticity, the deposition of ingredients, and mechanical resistance. The term „repair” can therefore be useful if it clearly specifies what has actually improved.
6. Does thicker hair mean the growth of new hair?
No. The increase in the strength of existing hair and the production of new hair by the hair follicles are different biological effects. Reducing brittleness can help maintain length and improve the density effect, but it does not show increased hair follicle activity. Research on hair growth requires other methods.
7. Is hydrolyzed keratin actually a standardized peptide?
No. Hydrolyzed keratin usually contains a mixture of protein fragments, not a single peptide with an identical sequence. Products may differ in molecular mass, charge, composition, and other properties.[2] The name of the ingredient itself does not mean that two products contain functionally identical material.
8. Are smaller peptides always better for hair?
No. A smaller size may affect the access to certain parts of the damaged fiber, but it does not guarantee a better result for every parameter. Material closer to the surface can also improve conditioning, reduce friction, or form a film. It is therefore important to determine which specific material improves a specific result under the appropriate conditions.
9. Does peptide penetration prove the repair of the bonds?
No. Penetration only shows that detectable material has reached a specific part of the fiber. It does not automatically indicate what chemical reactions occurred after it reached that part, nor whether the interrupted native peptide bonds were restored.
10. Does improved tensile strength mean less brittleness when combing?
No. The single fiber tensile test and the repeatable combing test produce different types of loads. The product may yield a favorable result in one test without being proportionally the same result in the other. The results should therefore be reported separately.
11. Does greater stiffness always mean better hair condition?
No. Stiffness is only one of the mechanical parameters. A stiffer fiber does not necessarily have to be more flexible, easier to style, more resistant to repeated combing, or less prone to cracking. The result should be interpreted in the context of the specific application.
12. Can spectroscopy prove the reconstruction of native peptide bonds?
It can provide important information about chemical changes, but the increase in signals associated with amide groups alone is not sufficient to demonstrate the reconstitution of the original keratin skeleton. The added peptide or protein material itself contains amide bonds, and crosslinking can lead to structures different from the native sequence. A stronger statement requires more specific structural evidence.
13. Does the effect lasting for five washes mean a permanent repair?
No. It simply means that in a specific study, the effect remained detectable after five washing cycles. [4] Other shampoos, water conditions, thermal styling, brushing, or further treatments can affect the result. Resistance to several washes and durable repair are not equivalent claims.
14. Does the product testing without rinsing confirm the effect of the rinsed product?
Not automatically. Products without rinsing and products rinsed provide different contact times, deposition levels, concentrations remaining on the hair, and exposure conditions. The evidence is strongest when the tested format corresponds to the product and method of use stated on the label.
15. Do cellular compatibility tests confirm full safety in humans?
No. Cell studies analyze selected biological responses under controlled laboratory conditions. They do not provide a complete assessment of safety in humans. Issues such as irritation of the scalp, allergies, repeated use, and individual susceptibility require data relevant to those specific issues.
16. Can the results obtained on chemically straightened hair be applied to hair that has been bleached?
They can serve as a basis for hypotheses, but it should not be assumed that they are transferred unchanged. Chemical straightening and highlighting lead to different exposure histories and can damage the hair through various chemical and structural processes. The results should therefore be contextualized according to the type of hair and the way it is damaged.
17. What evidence should accompany the declaration regarding the repair of peptide bonds?
A strong declaration should specify the exact product, type of damage, proposed mechanism related to the bandages, the comparative group, and the measured effect. If the declaration concerns specifically the reconstruction of the keratin skeleton, it should be supported by appropriate chemical and structural evidence, rather than solely improvements in smoothness or mechanical strength. The durability of the effect should also be evaluated separately. The most scientifically informative declaration is the precise one that does not go beyond what has actually been demonstrated by the methods used.
Summary
Products containing peptides can improve the measurable properties of damaged hair, but the term „repair of peptide bonds” requires much more specific evidence than just showing smoother hair, greater tensile strength, easier combing, or less brittleness.
This distinction is important because the improvement of hair properties can result from several different mechanisms.
Material containing peptides can settle on the surface, penetrate into accessible parts of the fiber, interact with keratin through noncovalent forces, form a film, or participate in specific chemically-mediated cross-linking processes.
These mechanisms should not be automatically reduced to a single explanation.
In particular surface attachment, penetration, hydrogen bonds, other non-covalent interactions, covalent cross-linking, and reconstruction of the original peptide backbone of keratin are separate mechanisms..
Evidence confirming one of them does not automatically confirm the others.
The studies also show why the exact characteristics of the material being tested are important.
Hydrolyzed keratin is not a standardized peptide.
Defined tripeptides can interact with hair differently than heterogeneous protein hydrolysates.
Systems containing network enzymes represent another type of intervention.
The formulation can alter the properties of the product, and the results obtained on chemically straightened hair, on fibers exposed to UV radiation, or in another specific model of damage should maintain this experimental context.
Similarly, the measured effect must be precisely defined.
Improving tensile strength is not the same as reducing brittleness when combing.
Less fragility is not evidence of increased hair growth from the follicles.
Maintaining the effect for several washes does not prove permanent repair.
Penetration does not automatically indicate what chemical effects occur inside the fiber.
The change in the spectroscopic signal associated with the amide groups does not in itself prove the reconstruction of the original keratin skeleton.
The appropriate conclusions remain therefore related to specific material, formulation, type of hair, comparison group, research method, and experimental conditions in which the result was obtained.
Product declarations are most informative when they explain exactly what has been improved, how this improvement was measured, with what product it was compared, under what conditions the result was obtained and for how long the effect lasted.
A more modest but well-documented declaration — like less brittleness, improved mechanical properties or better conditioning — may convey much more valuable information than a broad claim about „rebuilding connections” if the molecular mechanism itself has not been demonstrated.
The most important principle is simple:
The improvement in hair properties is evidence of an improvement in hair properties; the reconstruction of peptide bonds becomes evidence only when an appropriate chemical mechanism has also been demonstrated.
Disclaimer
This article is intended solely for educational and scientific-informative character. It explains the structure of the hair fiber, studies regarding peptides and keratin, mechanical tests, and terminology related to precursors, bonds, and the interpretation of cosmetic claims regarding hair regeneration.
The article does not promote or recommend any specific product for hair care, peptide ingredient, keratin treatment, repair bonding system, formulation, or commercial brand.
The results of laboratory tests regarding isolated hair fibers, hydrolyzed proteins, specific peptides, computer models, spectroscopy, or systems containing enzymes should not be automatically interpreted as evidence of the equivalent efficacy of similarly described products available for sale.
The improvement in the mechanical properties of the hair shaft does not mean treatment of hair loss, an increase in the activity of the hair follicles, or the treatment of scalp diseases.
Laboratory material testing does not provide a complete assessment of the safety, tolerance, or actual performance of the product during daily use. Therefore, statements regarding a specific product should be evaluated based on its actual formulation, intended use, available evidence, and the conditions under which it was tested.
References
- Yu, Y., Yang, W., Wang, B., & Meyers, M. A. (2017). Structure and mechanical behavior of human hair. Materials Science and Engineering: C, 73, 152–163. https://doi.org/10.1016/j.msec.2016.12.008
- Malinauskyte, E., Shrestha, R., Cornwell, P. A., Gourion-Arsiquaud, S., & Hindley, M. (2021). Penetration of different molecular weight hydrolysed keratins into hair fibres and their effects on the physical properties of textured hair. International Journal of Cosmetic Science, 43(1), 26–37. https://doi.org/10.1111/ics.12663
- Rha, C. S., In, B. G., Myoung, K., Song, C., Lee, E. S., Baek, H. S., & Park, W. S. (2026). Bio-active designed peptide for hair keratin strengthening. International Journal of Cosmetic Science. Advance online publication. https://doi.org/10.1111/ics.70092
- Liu, Y., Liu, J., & Xiao, J. (2023). Enzymatic crosslinking of amino acids improves the repair effect of keratin on hair fiber. Polymers, 15(9), Article 2210. https://doi.org/10.3390/polym15092210
- Fernandes, M. M., Lima, C. F., Loureiro, A., Gomes, A. C., & Cavaco-Paulo, A. (2012). Keratin-based peptide: Biological evaluation and strengthening properties on relaxed hair. International Journal of Cosmetic Science, 34(4), 338–346. https://doi.org/10.1111/j.1468-2494.2012.00727.x
- Fan, J., Wu, L., Wang, J., Bian, X., Chen, C., & Chang, K. (2025). Performance and mechanism of hydrolyzed keratin for hair photoaging prevention. Molecules, 30(5), Article 1182. https://doi.org/10.3390/molecules30051182