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

Wool fibers are composed of keratin proteins bundled into microfibrils.

—A. Goho

compare keratinocyte

keratinous

kə-ˈra-tə-nəs 

adjective

Examples of keratin in a Sentence

Recent Examples on the Web

According to Korean hair expert Hyerin Jeon, this shampoo features 10,000 ppm of 10 different proteins, including collagen and keratin, delivering salon-grade conditioning at home. —Iman Balagam, Vogue, 27 Apr. 2026

Researchers revealed that keratin – a natural structural protein derived from wool – was shown to support bone regeneration in a living animal. —Prabhat Ranjan Mishra, Interesting Engineering, 27 Apr. 2026

On the other hand, tape-ins are often well suited for straight to wavy hair types, and keratin bonds are great for curly or straight hair, but both are best applied by a professional. —Hunter Lacey, Allure, 9 Apr. 2026

This branch of medicine also studies hair and nails, because skin, hair, and nails are made of the same protein: keratin. —Encyclopedia Britannica, 2 Apr. 2026

Word History

Etymology

borrowed from German Keratin, from Greek kerat-, stem of kéras "horn" + German -in -in entry 1 — more at kerato-

Note: The term was introduced by the German physician and chemist Johann Franz Simon (1807-43) in Handbuch der angewandten medizinischen Chemie, 1. Theil, Medizinisch-analytische Chemie (Berlin, 1840), p. 49.

First Known Use

circa 1849, in the meaning defined above

Rhymes for keratin

• ferritin
• cytokeratin
• samaritan

Kids 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