keratin

noun

ker·​a·​tin ˈker-ə-tən How to pronounce keratin (audio)
: any of various sulfur-containing, fibrous, acidic or basic proteins chiefly of epithelial cells and tissues that are relatively insoluble and resistant to degradation, form filaments which assemble into bundles to provide structural support, and are the primary component of hair, nails, horns, claws, hooves, quills, scales, feathers and the epidermal layer of skin

Note: In addition to its structural properties, keratin also plays a role in cell growth and proliferation, cellular transport of substances, and intercellular communication.

Rhino horn is not actually horn but densely compacted fibers of keratin, a protein found in hair and fingernails.Maryanne Vollers
Wool fibers are composed of keratin proteins bundled into microfibrils.A. Goho
compare keratinocyte
keratinous adjective

Examples of keratin in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
The kit also includes ingredients such as argan oil, keratin, and ginseng root to help condition and strengthen hair. Nora Colomer, FOXNews.com, 28 Mar. 2025 Urea can also help remove keratin found in calluses and corns. Sherri Gordon, Health, 19 Mar. 2025 The keratin protein and jojoba oil in the serum strengthened and nourished our testers' weak, brittle nails, and their cuticles became noticeably healthier as well. Toni Sutton, People.com, 25 Feb. 2025 The formula features Virtue's signature alpha keratin protein, which staves off breakage, boosts volume, and moisturizes without weighing down hair. Annie Blackman, Allure, 14 Feb. 2025 See All Example Sentences for keratin

Word History

Etymology

borrowed from German Keratin, from Greek kerat-, stem of kéras "horn" + German -in -in entry 1 — more at kerato-

Note: The term was introduced by the German physician and chemist Johann Franz Simon (1807-43) in Handbuch der angewandten medizinischen Chemie, 1. Theil, Medizinisch-analytische Chemie (Berlin, 1840), p. 49.

First Known Use

circa 1849, in the meaning defined above

Time Traveler
The first known use of keratin was circa 1849

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Cite this Entry

“Keratin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/keratin. Accessed 5 Apr. 2025.

Kids Definition

keratin

noun
ker·​a·​tin ˈker-ət-ᵊn How to pronounce keratin (audio)
: a sulfur-containing protein that makes up hair and horny tissues (as nails)

Medical Definition

keratin

noun
ker·​a·​tin ˈker-ət-ən How to pronounce keratin (audio)
: any of various sulfur-containing fibrous proteins that form the chemical basis of horny epidermal tissues (as hair and nails) and are typically not digested by enzymes of the gastrointestinal tract see pseudokeratin

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