There are several possibilities for lumbar dermatitis and blackening: first, congenital abnormalities in pigment distribution, mostly found at an early age, with no specific cause and little harm to the body. Second, it may be related to repeated local friction, such as wearing tight pants, repeated contact with metal belts, etc. Third, it may be the pigmentation left after the inflammatory reaction, the waist is good for some, such as allergic dermatitis, shingles and other diseases, local inflammatory reaction easily left pigmentation, after 6-12 months can fade on their own, with such as arbutin whitening essence and other topical preparations may have some effect. Fourth, other causes of pigmentation is not obvious. After finding the waist blackening can be combined with the specific situation to analyze the possibility one by one, if necessary, go to the hospital for consultation.