Jock itch (tinea cruris) is a rash caused by a fungal infection. It occurs in the skin folds between the thigh and groin where it's warm and moist.
It starts as a small, red, itchy spot. It can grow larger in the shape of a round ring, 1 to 2 inches wide. It may cause the skin to flake. It may also spread to the scrotum, the skin that covers your testicles. This infection is treated with skin creams or oral medicine.