Darkening of the face may be caused by physiological factors such as exposure to the sun, or it may be caused by diseases such as acanthosis nigricans and melioidosis. 1. Physiological factors: If the facial skin is exposed to sunlight, it may lead to melanin proliferation, resulting in darkening of the complexion. 2. Acanthosis nigricans: Typical symptoms include dryness, roughness and deepening of the color of the skin, which can affect the whole body. Some patients are prone to darkening of the complexion. The cause of the disease is unknown and may be related to genetic and obesity factors. 3. Melanosis: It is a kind of disease caused by pigmentation, the cause of which is related to age, endocrine disorders and other factors, mostly seen in the face, colon and other parts. It can also cause darkening of the face. 4. Other diseases: darkening of the face also needs to consider the possibility of chronic kidney disease and other internal diseases. There are different reasons for the darkening of the face, after excluding physiological factors, you should go to the hospital for an interview and relevant examination, so as to facilitate the identification of the cause.