Understanding Hair Structure: Why Keratin Is Essential to Hair Health
To take good care of your hair, you must first understand what it is made of. Its strength, shine, and flexibility are not the result of chance: everything is based on a complex and unique structure, dominated by an essential protein… keratin .
The three layers of the hair fiber
A hair is not a simple fiber. It is composed of three distinct layers:
- The cuticle : the outermost layer, formed of scales that fit together like tiles. It protects the hair fiber and gives hair its shine and softness to the touch.
- The cortex : This is the main part of the hair, responsible for its strength and color (pigments). It also gives the hair its mechanical strength.
- The medulla : the innermost layer, present especially in thick hair.
Keratin, the heart of hair strength
Hair strength is mainly based on its chemical composition. Hair primarily contains:
- keratin proteins,
- lipids,
- and water.
Keratin is key: it is a unique protein, rich in cysteine, a sulfur-containing amino acid. This richness in cysteine distinguishes hair keratin from skin keratin (7.6% versus 2.9%).
Why is this important? Because cysteine forms disulfide bonds, true "bridges" that connect the keratin chains. These bridges give hair its strength, resilience, and durability.
An architecture reinforced by multiple links
La fibre capillaire est une véritable prouesse biologique :
- Les liaisons covalentes et les ponts disulfures assurent la solidité.
- Les liaisons ioniques et hydrogène donnent souplesse et élasticité.
- Les forces hydrophobes participent à la cohésion.
C’est grâce à ce réseau complexe que le cheveu peut à la fois être résistant et flexible. Son comportement varie en fonction de l’humidité : il peut s’allonger, gonfler ou s’assouplir.
Mais attention : lorsque les ponts disulfures sont détruits (par exemple lors d’une décoloration ou d’un lissage chimique), la fibre perd de sa force et devient cassante.
The role of lipids and water
Besides keratin, hair contains:
1 to 9% lipids, which provide shine, suppleness and a “silky” effect. They also act as a natural lubricant.
Up to 32% water, which contributes to flexibility and allows the formation of hydrogen bonds with proteins.
Why repairing your hair's keratin is essential
Les agressions quotidiennes (soleil, pollution, UV, chaleur des appareils, lavages fréquents, produits chimiques comme colorations ou lissages) endommagent la structure capillaire.
Résultat : cheveux secs, ternes, cassants, difficiles à coiffer.
La solution ? Apporter à la fibre capillaire des acides aminés soufrés biodisponibles, capables de restaurer les ponts disulfures et de régénérer la kératine endommagée.
C’est précisément ce que nous faisons en associant la kératine de laine bio et la bave d’escargot dans nos soins capillaires Mademoiselle Agathe : deux ingrédients naturels riches en peptides actifs, capables de pénétrer en profondeur pour redonner aux cheveux leur force et leur beauté originelle.
Hair health depends on a subtle balance between keratin, lipids, and water. Keratin, thanks to its richness in cysteine and disulfide bonds, is the central element of hair strength and shine.
By choosing treatments formulated with real animal keratin , compatible with human hair fiber, you offer your hair authentic and lasting repair — well beyond the surface effects of plant phytokeratin.
Malinauskyte E, Shrestha R, Cornwell PA, Gourion-Arsiquaud S, Hindley M. Penetration of different molecular weight hydrolyzed keratins into hair fibers and their effects on the physical properties of textured hair. Int J Cosmet Sci. 2021 Feb;43(1):26-37. doi:10.1111/ics.12663. Epub 2020 Oct 15. PMID: 32946595; PMCID: PMC7820954.
Fernandes et al., 2012 – Int. J. Cosmetic Science – Keratin-based peptide strengthens relaxed hair (mechanical & thermal recovery) link
Barba et al., 2010 – Fibers and Polymers – Wool keratin proteins restore major properties of pretreated hair.
Basit et al., 2018 – Biotechnology Reports – Recombinant keratin K31 improves smoothness, diameter and resistance of damaged hair.
Daniels et al., 2016 – IFSCC Magazine – Comparative study: hydrolyzed keratin vs wheat vs collagen. Keratin = best for wet tensile strength.
Cruz et al., 2017 – Int. J. Biol. Macromol. – Small peptides interact via hydrophobic bonds and disulfide bridges with human keratins.
Essendoubi et al., 2019 – Int. J. Cosmetic Science – Confocal Raman: monitoring α-helix/β-sheet conformations of hair keratin with active ingredients.
Fan et al., 2025 – Molecules – Hydrolyzed keratin prevents UV-induced hair photoaging.
