Keratin: The Protein Your Hair Is Made Of

Keratin is the protein your hair is built from, the same family that makes nails and the outer layer of skin. Hair is essentially keratin protein spun into fibres, bundled into a core, and armored with scales. Knowing that explains a lot about what hair products can and cannot do.

How keratin builds a strand

Keratin chains are wound into microscopic fibres, the fibres are bundled into the cortex, and the bundle is held together by disulfide bonds, the sulfur cross-links that give hair its strength. The outer cuticle scales are keratin too. So when hair is damaged, it is the keratin structure, and especially those cross-links, that has been broken.

Why "keratin treatments" mostly coat

It is tempting to think you can fix keratin damage by adding keratin. Size matters: small keratin peptides can penetrate damaged hair, while large proteins mostly stay near the surface (Malinauskyte et al. 2021); there is no single cut-off. They deposit on the surface, where they smooth and add temporary body, then wash off. That is useful conditioning, but it is not the same as rebuilding the broken structure inside.

What real repair requires

Treatments aimed at the cortex have to reach it: small peptides and reactive molecules designed to form new cross-links are the two main approaches, and ANATOMY's molecular reconstruction uses the second. The complete picture of damage and repair is in Hair Porosity: The Complete Science.

Reference

• Robbins, C.R. Chemical and Physical Behavior of Human Hair, 5th ed. Springer (2012).