from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A tough, insoluble protein substance that is the chief structural constituent of hair, nails, horns, and hooves.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A protein which hair and nails are comprised of.

from the GNU version of the Collaborative International Dictionary of English

  • n. A sulfur-containing fibrous protein constituting the main structural protein of hard epidermal tissues, such as horn, hair, feathers, nails, claws, hoofs, and the like. It is an insoluble substance, and, unlike elastin, is not dissolved even by gastric or pancreatic juice. By decomposition with sulphuric acid it yields leucine and tyrosine plus various other acid-stable amino acids. The amino acid composition varies, but it usually has a high percentage of cystine, which stabilizes and insolubilizes the protein by forming intrachain linkages. A softer form of keratin is present in the epidermis and whalebone. Called also epidermose.

from The Century Dictionary and Cyclopedia

  • n. Same as ceratin.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a fibrous scleroprotein that occurs in the outer layer of the skin and in horny tissues such as hair, feathers, nails, and hooves


from The American Heritage® Dictionary of the English Language, 4th Edition

Greek keras, kerāt-, horn + -in.


  • There are a number of hair-straightening salon treatments besides Brazilian Blowout on the market, some of which are called "keratin treatments" and "Brazilian treatments."

    Calls for FDA to Regulate Hair Straighteners

  • Hair is made up mostly of a protein called keratin, which is the same material that makes up hooves, claws and fingernails.

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  • The plate of the nail is composed of a substance called keratin, which is produced by amino acids.

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  • For example, Justin R. Barone, a research scientist at the U.S. Department of Agriculture’s Environmental Quality Laboratory in Beltsville, MD, and colleagues have found that chicken-feather keratin is ideal for strengthening composites.

    Chicken feathers no longer for the birds

  • This is when the buds of the tongue kick into overproduction of a substance called keratin, which causes the buds to grow longer than normal.

    Dr. Harold Katz: Bad Breath and Your Tongue

  • First my mother, then my aunt and a half dozen co-workers — all of them singing the praises of keratin, which is an extremely strong protein that makes up most of the composition of our hair and nails.

    Crazy for Keratin

  • As you can see in Figure 4.1, your nails are composed of laminated layers of a protein called keratin, which as you know by now is also found in your hair and skin.

    You Being Beautiful

  • That hair shaft is made up of a protein called keratin.

    You Being Beautiful

  • Nails and hair are made of a very different protein called keratin, and gelatin has no advantage over other protein sources in supplying the building blocks for keratin production.

    On Food and Cooking, The Science and Lore of the Kitchen

  • Cells that make up the stratum corneum contain keratin, which is a protein that keeps skin hydrated by preventing water from evaporating.

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