CosmeticBet
Conditioners

Hydrolyzed keratin

INCI: HYDROLYZED KERATIN · also Keratin peptides

Keratin protein in pieces: their size decides where they go.

How common

All products1.1%
In hair colours16%
In conditioners10%
In shampoos4.2%

163 of 14,784 products with a full ingredient list in Open Beauty Facts; No. 235 of all the names found on their labels.

What it is

  • Keratin protein broken into pieces (peptides). In the study below they came from wool.

    SourceHide
    wool derived hydrolysed keratins (i.e. peptides)[1] Study · 2021 · open source

Why it is in products

  • To condition skin and hair.

    SourceHide
    which function mainly as skin and hair conditioning agents in personal care products[2] US Cosmetic Ingredient Review expert panel · 2021 · open source

What it does

  • Size decides where it goes: in one lab study on relaxed curly hair, small and mid-size pieces went deep into the cortex, while large ones stayed on the surface.

    Some evidencehairSourceHide
    Low- and mid-MW compounds were able to penetrate deep into the hair cortex. High-MW peptide adsorbed onto the hair surface and possibly slightly penetrated into the outer layers of the fibre surface.[1] Study · 2021 · open source

  • In the same study, mid-size and large pieces made hair stiffer and reduced breakage, in both dry and humid air.

    Some evidencehairSourceHide
    Both mid- and high-MW keratin peptides, increased Young's modulus and reduced hair breakage at 20% and 80% relative humidity.[1] Study · 2021 · open source

Downsides and safety

  • The US expert panel found keratin ingredients safe as used.

    Well establishedSourceHide
    concluded that the 8 keratin-derived ingredients are safe in the present practices of use and concentration described in this safety assessment[2] US Cosmetic Ingredient Review expert panel · 2021 · open source

Where it works

Surface (cuticle)Inside (cortex)Core (medulla)

Small pieces get into the cortex; large ones stay on the surface.

Some evidenceSourceHide
Low- and mid-MW compounds were able to penetrate deep into the hair cortex.[1] Study · 2021 · open source

Rules

European Union

  • No EU limit: it is not on the regulation’s lists of banned or restricted substances, preservatives or UV filters.

    How we checkedHide
    We searched Annexes II to VI of the EU regulation (consolidated text of 18 May 2026): no entry.open the list

United States

  • Not on the FDA’s list of prohibited or restricted cosmetic ingredients. In the US, cosmetics and their ingredients (other than colour additives) don’t need FDA approval before sale.

    SourceHide
    Under U.S. law, cosmetic products and ingredients, other than color additives, do not need FDA approval before they go on the market[3] US Food and Drug Administration · open source
    We searched the FDA’s list of prohibited and restricted cosmetic ingredients: no entry.open the list

Sources

  1. Penetration of different molecular weight hydrolysed keratins into hair fibres and their effects on the physical properties of textured hair Malinauskyte E et al., International journal of cosmetic science, 2021StudyAuthors include staff of Croda (with TRI Princeton)
  2. Safety Assessment of Keratin and Keratin-Derived Ingredients as Used in Cosmetics International journal of toxicology, 2021US Cosmetic Ingredient Review expert panel
  3. Prohibited & Restricted Ingredients in Cosmetics | FDA US Food and Drug Administration

Checked against these sources on 4 November 2026. Spot a mistake? Tell us.