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

Example Sentences

Recent Examples on the Web Collagen supplements are often recommended for hair growth because collagen has many of the amino acids found in keratin, which is the primary protein found in hair. Sarah Anzlovar Ms, Health, 17 Mar. 2023 This formula relies on flaxseed and perilla seed oils to strengthen keratin, as well as skin-softening apricot seed oil to keep fingers in tip-top shape, and earned our coveted Best of Beauty Award in 2018. Alexis Rhiannon, Allure, 16 Mar. 2023 The shampoo and conditioner set features Karmatin, which is essentially a vegan keratin treatment that bonds to hair follicles and remains attached to strands even after rinsing. Nicol Natale, Peoplemag, 10 Mar. 2023 Or, opt for a product with allantoin, which Dr. Brazzo says can hydrate the skin, soften keratin, and promote healing. Sarah Bradley, Verywell Health, 6 Mar. 2023 Fendi, for whom fur is still a significant part of the business, has been experimenting with a new alternative using keratin, the main protein in hair. Nick Haramis Robbie Lawrence Hisato Tasaka, New York Times, 1 Mar. 2023 This Amazon bestseller features natural oils, including coconut oil, as well as vitamins, biotin, and keratin that thoroughly cleanse the scalp to create a clean slate for new growth to sprout. Nerisha Penrose, ELLE, 28 Feb. 2023 This one contains keratin and hydrating oils that repairs and nourishes your tired, depleted strands. ELLE, 23 June 2022 What happens is that the hair follicles on your body—especially around backs of the arms, thighs, buttocks, and even face—get plugged up with too much keratin or protein, and turn into small, hard bumps. Talia Abbas, Glamour, 19 July 2021 See More

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 1 Apr. 2023.

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

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