Pimples on the buttocks may be caused by AIDS, or folliculitis, eczema and other causes. 1.AIDS: Rash may appear in the early stage of AIDS, but it is mostly itchless red papules, occasionally herpes, the site is not fixed. If you want to clarify whether it is AIDS, you can go to the hospital to do HIV antibody test, if it is positive then it suggests that it may be infected with AIDS. 2. Folliculitis: acne on the buttocks may be caused by folliculitis, folliculitis is usually associated with local bacterial infection of hair follicles. Early clinical manifestations of red papules, gradually become papular pustules, with mild pain. Most can be self-healing, but easy to recur, usually without scarring. 3. Eczema: acne on the buttocks may also be caused by eczema, which is related to various internal and external factors. The patient’s lesions will appear red spots, papules, base red, gradually fused into a piece, often accompanied by obvious itching. When the symptoms of acne on the buttocks appear, if you want to clarify whether it is related to HIV infection, it is recommended to go to the hospital in time, improve the relevant examination to clarify the diagnosis, so as not to delay the condition.