a group of human and animal diseases of varying etiologies characterized by pathological changes in the skin and its appendages (nails and hair) and in the visible mucous membranes. In man, skin diseases are manifested by spots, vesicles filled with transparent fluid or pus (pustules), nodules elevated above the skin, scales formed by the desquamation of the horny layer of skin, scratches, ulcers, and cracks. Many skin diseases are accompanied by itching, a burning sensation, and pain.

Inflammatory skin diseases (dermatitises) result from direct exposure to chemicals, mechanical factors, radiation, or extremes of temperature. Other skin diseases are caused by metabolic disorders and by the functional impairment of the nervous and endocrine systems in diseases of the internal organs (for example, the liver and the gastrointestinal tract). A large group of skin diseases are classified as pyodermas (purulent diseases). Cutaneous tuberculosis is an infectious disease of the skin.

Skin diseases (for example, scabies) may be caused by parasitic insects or pathogenic fungi. Some skin diseases are manifestations of increased body sensitivity to various stimuli, including drugs and certain plants. Neoplasms such as birthmarks, warts, and tumors may develop on the skin. Dermatology is the science that studies skin diseases.