Definition of "keratin" []

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "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.""
• "Hair is made up mostly of a protein called keratin, which is the same material that makes up hooves, claws and fingernails."
• "The plate of the nail is composed of a substance called keratin, which is produced by amino acids."