Dark skin may be caused by physiological factors such as inadequate sun protection measures and heredity, as well as post-inflammatory hyperpigmentation and melanosis. 1. Physiological factors: If the daily sunscreen measures are not in place, ultraviolet radiation on the skin surface for a long time, may lead to the accumulation of melanin under the skin, so that the skin becomes dark; secondly, the dark skin color may also be affected by the parents of genetic factors. 2. Post-inflammatory hyperpigmentation: If you have ever suffered from eczema, contact dermatitis and other skin diseases in a large area, after the elimination of the disease, the affected area of the skin may appear post-inflammatory symptoms of hyperpigmentation, resulting in darker skin color. 3. Melanosis: lack of B vitamins in the body, long-term exposure to photosensitive substances and other reasons may induce melanosis, so that the patient appears black skin, dust-like skin debris on the surface of the skin and other symptoms. There are many reasons for dark skin, and we recommend that you go to the hospital after eliminating physiological factors to clarify the cause of the disease and follow the doctor’s instructions for treatment.