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 cottontail rabbit papillomavirus (CRPV) makes rabbits grow real horns made of keratin, mostly on their heads but sometimes on their faces.
—Popular Science Team, Popular Science, 23 Oct. 2025
Scroll to shop our most popular picks, from keratin-rich hair masks, to lightweight oils.
—Conçetta Ciarlo, Vogue, 8 Oct. 2025
This lightweight leave-in serum smooths and seals split ends on contact, while the brand’s signature alpha keratin 60ku protein repairs damage from the inside out.
—Christa Joanna Lee, Allure, 30 Sep. 2025
An excess of keratin, a protein found in hair, causes tiny red bumps that look like goosebumps.
—Carrie Madormo, Health, 10 Sep. 2025
See All Example Sentences for keratin
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Popular Science Team, Popular Science, 23 Oct. 2025
Scroll to shop our most popular picks, from keratin-rich hair masks, to lightweight oils.
—Conçetta Ciarlo, Vogue, 8 Oct. 2025
This lightweight leave-in serum smooths and seals split ends on contact, while the brand’s signature alpha keratin 60ku protein repairs damage from the inside out.
—Christa Joanna Lee, Allure, 30 Sep. 2025
An excess of keratin, a protein found in hair, causes tiny red bumps that look like goosebumps.
—Carrie Madormo, Health, 10 Sep. 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 4 Nov. 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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