keratin
noun
ker·a·tin
ˈker-ə-tən 
: 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
Maryanne VollersWool fibers are composed of keratin proteins bundled into microfibrils.—A. Goho
compare keratinocyte
A. GohoExamples of keratin in a Sentence
Recent Examples on the Web
The powder's keratin fibers attach to your hair to help build and strengthen strands, lending a look of fullness and volume, especially when used over time.
—Deanna Pai, Allure, 21 Feb. 2025
Hydrolyzed keratin reinforces the nail’s structure, while biotin boosts keratin production for overall strength.
—Iman Balagam, Vogue, 15 Feb. 2025
To get more technical, your body overproduces keratin (the protein that forms the hard, outer layer of skin) in response to stressors like frequent walking, standing, and certain medical issues (more on that later).
—Jenna Ryu, SELF, 9 Jan. 2025
Chia seed oil, hydrolyzed keratin, and biotin—found in this shampoo and its perfect match, OUAI Fine Hair Conditioner—strengthen the hair cuticle and bring dull strands back to life.
—Christa Joanna Lee, Allure, 9 Feb. 2025
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Deanna Pai, Allure, 21 Feb. 2025
Hydrolyzed keratin reinforces the nail’s structure, while biotin boosts keratin production for overall strength.
—Iman Balagam, Vogue, 15 Feb. 2025
To get more technical, your body overproduces keratin (the protein that forms the hard, outer layer of skin) in response to stressors like frequent walking, standing, and certain medical issues (more on that later).
—Jenna Ryu, SELF, 9 Jan. 2025
Chia seed oil, hydrolyzed keratin, and biotin—found in this shampoo and its perfect match, OUAI Fine Hair Conditioner—strengthen the hair cuticle and bring dull strands back to life.
—Christa Joanna Lee, Allure, 9 Feb. 2025
See All Example Sentences for keratin
Cite this Entry
“Keratin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/keratin. Accessed 12 Mar. 2025.
Copy CitationKids Definition
keratin
noun
ker·a·tin
ˈker-ət-ᵊn
: a sulfur-containing protein that makes up hair and horny tissues (as nails)
Medical Definition
keratin
noun
ker·a·tin
ˈker-ət-ən
: 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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