Ringworm Jock itch, athlete's foot, and ringworm are all types of fungal skin infections known collectively as tinea. They are caused by fungi called dermatophytes that live on skin, hair, and nails and thrive in warm, moist areas. Symptoms of these infections can vary depending on where they are on the body. The source of the fungus is usually the soil, an animal (usually a cat, dog, or rodent), or most often, another person. Minor trauma to the skin (for instance, scratches) and poor skin hygiene increase the potential for infection.