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
Estrogen is also important in producing a protein called keratin that’s made in the nail bed.
—Jocelyn Solis-Moreira, Flow Space, 13 Feb. 2026
Rosemary oil—one of the key ingredients in the mask—is like hair-growth gold, but ceramides, jojoba, and keratin are also present in the strengthening and thickening formula.
—Kaitlin Clapinski, InStyle, 10 Feb. 2026
And because the fibers are hollow (unlike synthetic fibers) and the keratin in them isn’t compatible with odor-causing bacteria, this sweater is breathable and stays fresh in between its infrequent washings.
—Katie Jackson, Travel + Leisure, 5 Feb. 2026
With hydrolyzed silk and hydrolyzed keratin to strengthen and repair, the spray provides all-day hold while keeping hair touchable and soft.
—Conçetta Ciarlo, Vogue, 15 Jan. 2026
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Jocelyn Solis-Moreira, Flow Space, 13 Feb. 2026
Rosemary oil—one of the key ingredients in the mask—is like hair-growth gold, but ceramides, jojoba, and keratin are also present in the strengthening and thickening formula.
—Kaitlin Clapinski, InStyle, 10 Feb. 2026
And because the fibers are hollow (unlike synthetic fibers) and the keratin in them isn’t compatible with odor-causing bacteria, this sweater is breathable and stays fresh in between its infrequent washings.
—Katie Jackson, Travel + Leisure, 5 Feb. 2026
With hydrolyzed silk and hydrolyzed keratin to strengthen and repair, the spray provides all-day hold while keeping hair touchable and soft.
—Conçetta Ciarlo, Vogue, 15 Jan. 2026
See All Example Sentences for keratin
Cite this Entry
“Keratin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/keratin. Accessed 15 Feb. 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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