Blackening of the buttocks after sitting for a long time is due to excessive pigmentation caused by long-term frictional stimulation of the buttock skin. Patients need to avoid sitting for a long time and use topical drugs to deal with the situation as follows: 1. Avoid sitting for a long time: so that the buttock skin can reduce local friction and other stimuli and not easily aggravate pigmentation again; 2. Use topical drugs: clinically commonly used are vitamin E milk, which has the effects of emolliency, antioxidation and pigmentation fading, and hydroquinone cream for pigmentation diseases can also be used for decolorization treatment.