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

Keratin creates a dense, mineralized barrier over the tooth's surface, blocking the nerve channels responsible for sensitivity.

From Science Daily • Nov. 10, 2025

Keratin is durable and flexible, which made baleen a popular by-product of 19th-century whaling.

From Scientific American • Dec. 8, 2021

Keratin is same protein that makes up our fingernails and hair.

From BBC • Aug. 19, 2021

Karla bought Keratin to straighten her hair, had her eyebrows shaped, and applied fake nails with swirls of rhinestones.

From National Geographic • Jan. 27, 2021

Keratin, a substance forming the chief constituent in the hair, nails, and horn of animals.

From The Nuttall Encyclopædia Being a Concise and Comprehensive Dictionary of General Knowledge by Nuttall, P. Austin