Daily foot soak feet become black, may be related to the color factor of the foot soak, may also be related to the incorrect way of soaking and washing. 1. Drug factors. Part of the drug or foot powder with certain pigment, long time soaking may lead to local skin staining, such as potassium permanganate solution, coral ringworm net and so on. 2. Incorrect soaking. Due to the soaking process massage leads to subcutaneous blood vessel damage caused by bleeding, the recovery period may also be manifested as local skin blackening. Especially for some people with coagulation disorders, the chances of subcutaneous bleeding will be significantly higher. Due to the individual differences in clinical manifestations, a doctor’s consultation is required for specific cases.