keratin

American  

[ker-uh-tin] / ˈkɛr ə tɪn /

noun

1. a fibrous, structural protein that is the principal constituent of hoofs, nails, claws, talons, bills, horn, hair, feathers, etc., and that is found in the outermost layers of skin.

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keratin British  

/ ˈkɛrətɪn /

noun

1. a fibrous protein that occurs in the outer layer of the skin and in hair, nails, feathers, hooves, etc

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keratin Scientific  

/ kĕr′ə-tĭn /

1. Any of a class of tough, fibrous proteins that are the main structural component of hair, nails, horns, feathers, and hooves. Keratins are rich in sulfur-containing amino acids, especially cysteine. Individual keratin molecules are entwined helically around each other in long filaments, which are cross-linked by bonds between sulfur atoms on different chains. The twining and cross-linking produce strength and toughness.

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Etymology

Origin of keratin

First recorded in 1840–50; kerat- + -in ²

Explanation

Keratin is the name of the protein that forms your hair and fingernails. You've got something in common with spiders, too — their silk is also made from keratin. Keratin is a hard, fibrous protein that gives structure to certain body parts in humans and animals. Your toenails are made up of keratin, and so are your cat's claws. Horns, nails, hair, feathers, shells, and beaks — all of these are composed of keratin. The word comes from the Proto-Indo-European root ker, meaning "horn," followed by the scientific suffix -in, denoting a chemical.

Example Sentences

Biotin, also known as vitamin B7, helps the body produce proteins such as keratin, which supports hair, skin and nails.

From Science Daily • May 7, 2026

Researchers have found that toothpaste made from keratin, a protein naturally present in hair, skin, and wool, could both protect and repair damaged teeth while offering a sustainable alternative to traditional dental treatments.

From Science Daily • Nov. 10, 2025

In their study, published in Advanced Healthcare Materials, the scientists extracted keratin from wool.

From BBC • Aug. 13, 2025

Their horns are made of keratin, like human fingernails, and the procedure is not thought to be painful.

From Salon • Jun. 16, 2025

Peter Pauling arrived with the inside news that his father was preoccupied with schemes for the supercoiling of a-helices in the hair protein, keratin.

From "Double Helix" by James D. Watson