Darker and darker skin may be due to physiological reasons such as excessive exposure to sunlight, etc., and may also be due to pathologic reasons such as medication factors, melanosis, acanthosis nigricans, etc. 1. Physiological reasons Excessive exposure to sunlight: long exposure to ultraviolet rays can increase the activity of melanin in the skin, thus leading to darker and darker skin. 2. Pathological causes (1) Drugs: prolonged use of anti-tumor drugs such as cisplatin or antibiotics such as levofloxacin can increase the synthesis of melanin, resulting in skin pigmentation, leading to darker and darker skin. (2) Melanosis: Melanosis, also known as melanosis, the etiology and pathogenesis of which are still unclear, most patients have a history of exposure to photosensitive substances, and it can also be caused by the use of poor-quality cosmetics. (3) Acanthosis nigricans: Acanthosis nigricans is a skin disease characterized by downy or papillary hyperplasia, hyperkeratosis, and hyperpigmentation of the skin, which may be related to heredity, obesity, and diabetes mellitus, etc. It may appear as a deepening of the skin’s color, which is light grey, light brown, or dark brown. Skin is getting darker and darker if physiological reasons are excluded, it is recommended to go to the hospital in a timely manner to clarify the cause of the disease, and under the guidance of the doctor to carry out active treatment.