Keratin
Keratin is the fibrous protein hair is made of. Learn how its structure gives hair strength, what damages it, and what keratin treatments really involve.
Supriya Bhandary
Founder, Soumm · 4 September 2026 · Updated 14 October 2026
What is keratin?
Keratin is the fibrous structural protein that makes up most of the hair shaft, as well as nails and the outer layer of the skin. In hair, keratin chains are tightly bundled and linked by strong disulphide bonds, which give the fibre its strength and shape. (Wolfram, 2003)
What damages keratin
Bleaching, perming, chemical straightening, high heat and sunlight break bonds within the fibre, leaving hair weaker, rougher and more prone to breakage.
The hair shaft is not living tissue, so this damage cannot repair itself. It grows out as new hair replaces it.
About keratin treatments
Salon keratin smoothing treatments coat and reshape the hair, and some products release formaldehyde when heated. The US Food and Drug Administration has warned about formaldehyde exposure from such products. (US FDA)
See also: Cuticle, Breakage.
Sources
Wolfram LJ. Human hair: a unique physicochemical composite. J Am Acad Dermatol. 2003;48(6 Suppl):S106–14.
Questions
Yes. Keratin proteins make up most of the hair shaft.
Damaged hair cannot heal itself. Conditioners and oils can smooth and protect the fibre, but the damage only disappears as new hair grows.
Some smoothing treatments release formaldehyde when heated, which regulators have warned about. Check the ingredients and ask your salon about ventilation and formaldehyde-free options.