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
Ingredient-wise, Flores notes that it’s packed with argan oil, three types of honey, royal jelly, propolis, silk, and hyaluronic acid, along with keratin, ceramides, and rose extract to strengthen and moisturize strands.
—Iman Balagam, Vogue, 27 Dec. 2025
The secret weapon in question is bioactive keratin ferment, which manages to match proteins native to human hair while delivering vital nutrients straight to each strand’s cortex.
—Stacia Datskovska, Footwear News, 27 Dec. 2025
It’s designed with a simple and effective formulation featuring key ingredients such as vitamin B5, green tea extract, and myristoyl pentapeptide-17, a peptide that enhances keratin production to encourage hair growth (and strength).
—Jessie Quinn, StyleCaster, 15 Dec. 2025
Unlike texture release or keratin treatments, this one doesn’t require putting heat on the hair and isn’t intended to change or manipulate one’s hair texture.
—Annie Blay-Tettey, Allure, 15 Dec. 2025
See All Example Sentences for keratin
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Iman Balagam, Vogue, 27 Dec. 2025
The secret weapon in question is bioactive keratin ferment, which manages to match proteins native to human hair while delivering vital nutrients straight to each strand’s cortex.
—Stacia Datskovska, Footwear News, 27 Dec. 2025
It’s designed with a simple and effective formulation featuring key ingredients such as vitamin B5, green tea extract, and myristoyl pentapeptide-17, a peptide that enhances keratin production to encourage hair growth (and strength).
—Jessie Quinn, StyleCaster, 15 Dec. 2025
Unlike texture release or keratin treatments, this one doesn’t require putting heat on the hair and isn’t intended to change or manipulate one’s hair texture.
—Annie Blay-Tettey, Allure, 15 Dec. 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 1 Jan. 2026.
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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