The common causes of red buttocks are allergic dermatitis, folliculitis, jock itch and so on. 1. Allergic dermatitis: if you don’t pay attention to personal hygiene, don’t take a bath for a long time or wear underwear made of not very good material, it may induce allergic dermatitis in the buttocks, which in turn causes itchy buttocks as well as the manifestation of windy doughnut-like erythema. 2. Folliculitis: due to prolonged sitting, excessive sweating, wearing tight pants, etc., resulting in the buttocks in a long time in a humid and hot environment, and then bacterial infection. Its common manifestation is red follicular papules on the buttocks with itching. 3. ringworm: due to dermatophyte infection, mainly between people contact spread, can also be infected by tinea pedis, often manifested as ring or semi-ring erythema, pimples and consciously itchy feeling. So it can also lead to a red piece of buttocks especially itchy. All in all, if the buttocks red a special itch, it is recommended to go to the regular hospital in time, clear cause and targeted treatment.