Darkening of the skin on the posterior lumbar region can be seen as a result of skin pigmentation triggered by skin injury, which can be induced by factors such as friction and burns. The black pigmented area on the skin surface is characterized by irregular edges and smooth surface skin, mostly without symptoms that are not easily detected in time. Most of these cases are stable and do not need to be treated with medication. For skin surface ulceration, local elevation, skin color gradually aggravated phenomenon, you need to go to the dermatology department as soon as possible to perform skin biopsy to clarify the condition. If necessary, you can take oral vitamin C medication, which has a good inhibitory effect on the melanin on the skin surface. Pay attention to avoid long-term skin friction on the back of the waist, or local skin exposure to high temperature objects.