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

In a behind-the-scenes video, the teeth are labelled ‘baleen’, as in baleen whales, real-life marine mammals that have tough but flexible keratin hairs inside their mouths that filter their tiny fishy prey from the inflow of seawater. —Popular Science, 6 Mar. 2024

The collection is made with a custom technology: a bioactive keratin ferment. —USA TODAY, 20 Feb. 2024

Best of all, this shampoo is great for all types of curls and is suitable to use on hair that’s been treated with keratin, chemicals, and color. —Sophie Dodd, Peoplemag, 14 Jan. 2024

It’s enriched with a blend of growth-supporting ingredients, such as keratin and biotin. —Jessie Quinn, Peoplemag, 13 Feb. 2024

These hair vitamins contain a powerful blend of biotin, keratin, and collagen, along with essential vitamins, minerals, and antioxidants that infuse your hair with nutrients and promote growth. —Amber Smith, Discover Magazine, 3 Aug. 2023

At each of your fingertips there’s an ever-growing, translucent plate of fibrous protein called keratin, otherwise known as a nail. —Sabrina Sholts, Smithsonian Magazine, 12 Mar. 2024

The volumizing formula is enhanced with hydrating hyaluronic acid, vitamin E, and keratin to boost shine and lash thickness while replenishing brittle lashes. —Sophie Dodd, Peoplemag, 7 Jan. 2024

Hair dye, scissors, and keratin treatments do not evaporate once someone enters into their second Saturn Return. —Daniel Rodgers, Vogue, 23 Feb. 2024

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

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