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 This warm brown shade is vibrantly pigmented to make lashes look thicker and fuller, plus its formula is enriched with keratin and shea butter to condition each eyelash. Jennifer Hussein, Allure, 6 July 2024 Eventually, a subset of carnivorous dinosaurs, including sickle-clawed raptors and prehistoric precursors to birds, evolved complex feathers made of keratin, the same fibrous protein that makes up the hair and fingernails of people., 3 July 2024 The Oribe Signature Complex, a combination of watermelon, lychee, and edelweiss flowers, works to defend hair follicles from the deterioration of natural keratin, keeping the hair shaft stronger and more resilient. Carrie Honaker, Southern Living, 24 June 2024 The brick-and-mortar foray comes on the heels of Virtue’s launch of its Damage Reverse Serum, a leave-in treatment featuring the brand’s highest concentration of its proprietary alpha keratin 60ku protein. Noor Lobad, WWD, 18 June 2024 See all Example Sentences for keratin 

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'keratin.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


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

Dictionary Entries Near keratin

Cite this Entry

“Keratin.” Dictionary, Merriam-Webster, Accessed 21 Jul. 2024.

Kids Definition


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


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

More from Merriam-Webster on keratin

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