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keratosis ker·a·to·sis (kěr'ə-tō'sĭs)
n. pl. ker·a·to·ses (-sēz)
Excessive growth of horny tissue of the skin.
any protuberance on the skin resulting from the overdevelopment of the horny outermost covering of the skin, or epidermis, the main constituent of which is the protein keratin, which is synthesized in special cells of the skin, the keratinocytes. More generally, keratosis is any skin disorder attended by horny growths. The causes and lesions characteristic of keratotic skin disorders are varied, giving rise to some 20 different forms of keratosis; the more common ones are as follows: