Tinea cruris, also known as jock itch, is a common type of contagious, superficial fungal infection of the groin and buttocks region, which occurs predominantly but not exclusively in men and in hot-humid climates.

Typically, over the upper inner thighs, there is an intensely itchy red raised rash with a scaly well-defined curved border. It is often associated with athletes foot and fungal nail infections, excessive sweating, and sharing of infected towels or sports clothing. It is uncommon in children.

Its appearance may be similar to some other rashes that occur in skin folds including candidal intertrigo, erythrasma, inverse psoriasis and seborrhoeic dermatitis. Tests may include microscopy and culture of skin scrapings.

Treatment is with topical antifungal medications and is particularly effective if symptoms have recent onset. Prevention of recurrences include treating concurrent fungal infections and taking measures to avoid moisture build-up including keeping the groin region dry, avoiding tight clothing and losing weight if obese.