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Cosmetic ingredient

Proteins (hydrolysed keratin, wheat, silk…)

Conditioning and temporary "repair" for damaged or bleached hair Also on labels as: hydrolysed keratin, hydrolyzed wheat protein, silk amino acids, hydrolysed collagen

Reviewed on

What it does

Hair is mostly a protein called keratin, so it's no surprise products add proteins — usually hydrolysed (broken into smaller pieces). Reviews say smaller fragments can get into the hair, especially damaged or bleached hair, where more protein is deposited, while larger ones coat the surface.

What they can do is help temporarily: a dermatology review describes proteins in conditioners holding split-end fragments together until the next shampoo. Another review is blunt that amino acids "do not replace or restore" damaged hair structure. In a lab study funded by an ingredient supplier, some sizes of keratin fragment made relaxed, textured hair stiffer and less likely to break.

So "rebuilds", "repairs" and "restores" claims are best read as "makes damaged hair behave better for a while".

Cautions

  • Allergy: protein hydrolysates in hair conditioners have caused contact urticaria (hives), particularly in people with atopic eczema. Hydrolysed wheat protein in a facial soap caused an outbreak of wheat allergy in Japan. If you have eczema or a wheat allergy, check labels and patch-test.

How strong is the evidence?

Evidence: Cosmetic

Changes how hair looks or feels; not a treatment for any condition.

Evidence for the benefits comes from laboratory studies on hair fibres; there's no good clinical evidence of lasting repair. Rated cosmetic.

Products on this site that list it

Not medical advice. This guide is general information from the sources listed, not a diagnosis or a substitute for a pharmacist, GP or dermatologist. If you are worried, or symptoms are severe or not improving, get advice. Read our health information policy.

Sources

  1. Gavazzoni Dias MF. Hair cosmetics: an overview. Int J Trichology 2015 pmc.ncbi.nlm.nih.gov
  2. D'Souza P, Rathi SK. Shampoo and conditioners: what a dermatologist should know? Indian J Dermatol 2015 pmc.ncbi.nlm.nih.gov
  3. Malinauskyte E et al. Penetration of different molecular weight hydrolysed keratins into hair fibres. Int J Cosmet Sci 2021 pmc.ncbi.nlm.nih.gov
  4. Niinimäki A et al. Contact urticaria from protein hydrolysates in hair conditioners. Allergy 1998 pubmed.ncbi.nlm.nih.gov
  5. Yagami A et al. Outbreak of immediate-type hydrolyzed wheat protein allergy due to a facial soap in Japan. J Allergy Clin Immunol 2017 pubmed.ncbi.nlm.nih.gov