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
Because hair is made up of protein—specifically keratin—this is major, and can help prevent hair from becoming brittle and breaking.
—Jenn Barthole, Glamour, 28 May 2025
Now that the bone is finished healing and the keratin is growing, the team will mostly have to be patient.
—Laura Baisas, Popular Science, 10 Apr. 2025
Even feathers, which seem delicate, are made of keratin and are engineered for both insulation and lift without adding unnecessary bulk.
—Scott Travers, Forbes.com, 31 May 2025
Estrogen and testosterone both stimulate the production of keratin and contribute to the smooth, firm appearance of toenails and fingernails.
—Catherine Moyer, Verywell Health, 22 May 2025
See All Example Sentences for keratin
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Jenn Barthole, Glamour, 28 May 2025
Now that the bone is finished healing and the keratin is growing, the team will mostly have to be patient.
—Laura Baisas, Popular Science, 10 Apr. 2025
Even feathers, which seem delicate, are made of keratin and are engineered for both insulation and lift without adding unnecessary bulk.
—Scott Travers, Forbes.com, 31 May 2025
Estrogen and testosterone both stimulate the production of keratin and contribute to the smooth, firm appearance of toenails and fingernails.
—Catherine Moyer, Verywell Health, 22 May 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 19 Jun. 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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