intransitive verb
Definition: To produce a tough protein that is found in skin, hair, and nails, or to change into a form that contains this protein.
Example: As the skin cells mature, they begin to keratinize, forming a protective layer.
transitive verb
Definition: To change something into a tough protein called keratin, which is found in hair, nails, and skin.
Example: The skin cells will keratinize to form a protective barrier.