Definition of "keratinize" []

• To produce keratin or become like keratin. (verb-intransitive)
• To convert (something) into keratin. (verb-transitive)

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.

• "[1] As the cells in the three regions begin to keratinize and harden, they are integrated into the dead (keratinized) portion of the hair fiber; new hair cells in the hair bulb region push the dead shaft upwards towards the skin's surface."