The darkening of the face may be caused by physiological factors such as long-term sun exposure, or it may be caused by diseases such as acanthosis nigricans and solar dermatitis. 1. Physiological factors: If you are exposed to strong ultraviolet rays for a long time, it may cause your face to become darker and darker. 2. Acanthosis nigricans: mainly manifested as deepening of skin color, dryness and roughness, etc. The formation of acanthosis nigricans may be related to genetic defects, obesity and other factors. 3. Solar dermatitis: clinical manifestations of local flaking, hyperpigmentation and burning sensation, some patients may appear face is getting darker and darker. The formation of the disease is mostly related to excessive exposure to ultraviolet radiation. The cause of the increasingly dark face is not a reason, in the exclusion of physiological factors, it is recommended that patients seek medical examination to identify the cause.