Pigment is found in the cytoplasm of melanocytes in the basal layer of the epidermis. When UV rays are exposed to the skin, melanocyte synthesis of melanin increases, which causes the skin to darken. There are many reasons for the increase in pigmentation, which are as follows. 1. Sunlight irradiation: sunlight irradiation is the most common cause of melanin increase, ultraviolet radiation, the skin through the synthesis of melanin to reduce the damage of ultraviolet radiation on the skin, long-term ultraviolet sun exposure may also cause melanocyte malignant changes. 2. Some endocrine diseases such as hypoadrenalism and oral contraceptives. 3. Vitamin deficiency can also cause skin pigmentation, should eat more vegetables and fruits to avoid vitamin deficiency. 4. Chronic dermatitis or eczema, prolonged delay can also cause skin pigmentation.