ichthyosis /ik′thē·ō″sis/ [Gk, ichthys, fish, osis, condition] , any of several inherited dermatological conditions in which the skin is dry and hyperkeratotic, resembling fish scales. It usually appears at or shortly after birth and may be part of one of several rare syndromes. Some types respond temporarily to urea or lactic acid emollients. A rare, acquired variety accompanying a lymphoma or multiple myeloma occurs in adults. Also called fish skin disease, xeroderma. −ichthyotic, adj.