The reasons why the cotton ball turns black when iodine volt is wiped are as follows: First, it may be caused by sweaty skin, which can cause the cotton ball to turn black when the skin is disinfected with iodine volt after sweating. Second, the local skin epidermis off caused by the body’s metabolism will cause skin cell necrosis, cell shedding, long-term accumulation will lead to skin darkening, in the use of iodine disinfection will lead to the cotton ball black. Third, the skin is not clean caused by the skin may be stained with some substances, is the use of cosmetics or long time not clean caused by the use of iodine volt wipe, resulting in the cotton ball black. Fourth, there are some drugs in contact with iodine volts will be a chemical reaction resulting in blackening, such as sulfonamides, such as triclopidine, metronidazole, Levanox solution, hyoscine, etc. Patients should clean the skin before using iodine volts. Patients should pay attention to the cleanliness and hygiene of the skin in general, local unhygienic may lead to bacterial or viral infection and cause disease. Iodophor should not be used for a long time, it will lead to pigmentation and long-term use will lead to darkening of the skin.