Diffuse mastocytosis: A form of mastocytosis in which the entire skin is thickened and leathery with generalized reddening and intense pruritus (itching) due to widespread infiltration of the skin with mast cells.

Treatment may include antihistamines, drugs to reduce stomach acid, migraine headache drugs for headache, and cromolyn for bowel symptoms.

Also called diffuse cutaneous mastocytosis.