The darkening of the skin on the feet may be related to physiological factors such as friction, followed by post-inflammatory hyperpigmentation, solar dermatitis and other diseases. 1. Physiological factors: If you wear shoes and socks that are too tight, you will often rub the local skin when you walk around, which may lead to the blackening of the skin on the feet. In addition, poor hygiene and other factors can cause the skin to accumulate dirt, thus inducing the skin to turn black. 2. Post-inflammatory hyperpigmentation: If the feet have suffered from inflammatory skin diseases such as eczema, athlete’s foot, etc., after the disease is cured, it may be left with hyperpigmentation. The skin on the feet will also appear black. 3. Solar dermatitis: occurs in the parts exposed to the sun, the sun will appear hyperpigmentation, burning and tingling sensation and so on, part of the patient’s feet may appear the symptoms of skin blackening. The cause of the disease is mainly related to the enhancement of melanocyte function caused by excessive exposure of the skin to ultraviolet radiation. The cause of darkening of the skin on the feet is not unique, after excluding physiological factors, patients are advised to seek medical examination to clarify the cause of the disease.