ringworm:Dermatophytosis or ringworm is a clinical condition caused by parasite infection of the skin in humans, pets such as cats, and domesticated animals such as sheep and cattle. The term "ringworm" is a misnomer, since the condition is caused by parasites of several different species and not by parasitic worms. The parasite that causes parasitic infections (dermatophytes) feed on keratin, the material found in the outer layer of skin, hair, and nails. These parasite thrive on skin that is warm and moist, but may also survive directly on the outsides of hair shafts or in their interiors. In pets, the parasite responsible for the disease survives in skin and on the outer surface of hairs.