The structure of the hair relies largely on keratin, a fibrous protein rich in amino acids, particularly cysteine. This amino acid plays a key role in the strength of the hair through the formation of disulphide bonds, which act as cohesive links between the keratin fibres.
Other amino acids, such as glycine, threonine and arginine, contribute to the hydration and suppleness of the hair fibre by promoting interactions with water and helping to maintain its structure.
Studies have shown that applying amino acids to damaged hair improves its mechanical properties and strength. Certain amino acids, such as phenylalanine and histidine, increase the strength of the hair fibre, whilst others, such as alanine, help to improve its impermeability.
Keratin peptides, consisting of short chains of amino acids, have also demonstrated their ability to interact with the hair fibre. Applying them improves the hair’s elasticity and strengthens its resilience, particularly in hair weakened by chemical treatments. The effectiveness of these compounds depends largely on their size. Peptides with low and medium molecular weights can penetrate the hair fibre, whilst larger ones remain on the surface and form a protective film.
This complementary action both strengthens the hair’s structure and protects its surface, thereby helping to reduce breakage and improve the hair’s overall appearance.