Buttock redness is the erythema of the buttocks, which can be caused by contact dermatitis, or diaper dermatitis in the case of infants, and needs to be analyzed specifically according to the symptoms. 1. contact dermatitis: may be underwear dye allergy, lesions can be pants-shaped distribution, clear boundaries of the erythema, on which there are papules and pimples, severe redness and swelling and blisters and blisters, the latter blisters wall tension, the content of the clear, ruptured vesicles, and occasionally tissue necrosis can occur. 2. Diaper dermatitis: diaper replacement is not diligent, ammonia-producing bacteria decomposition of urine produced by ammonia stimulation of the skin, part of the diaper material related. It mostly involves the perineum of infants and may spread to the buttocks. The lesions are large and flushed, and may include macules and papules with clear margins and a pattern consistent with the extent of the diaper coverings. Buttock erythema may also have other causes, it is recommended to actively seek medical attention to clarify the cause of the disease and follow the doctor’s instructions for targeted treatment.