(1) Hypertrophy of the horny layer of the epidermis.
(2) Appearance of thickened, horny, verruca-like scales (for example, warts and calluses) over the entire body, concentrated in flexural areas.
(3) A condition marked by thickening of the outer layer of the skin, which is made of keratin (a tough, protective protein). It can result from normal use (corns, calluses), chronic inflammation (eczema), or genetic disorders (X-linked ichthyosis, ichthyosis vulgaris).
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