The sudden appearance of black tongue can be divided into physiological, pathological reasons, and some of the tongue blackened is caused by pharmacogenetic. 1. Physiological reasons: if you eat some black food such as mulberry, or just finished drinking soup, may cause a short period of black tongue, this situation generally lasts for a few hours or 1 ~ 2 days, can subside on their own. 2. Pathological reasons: some people with low immunity are prone to bacterial overpopulation, when the color of black bacteria or metabolites for black, there will be black tongue. 3. Pharmacogenetic reasons: long-term use of antibiotics is very easy to cause flora imbalance, may also cause black tongue, such as long-term use of penicillin caused by oral flora imbalance will cause black mold overpopulation, thus causing black tongue. In addition to the above factors, it is not excluded that it is caused by other factors. It is recommended that the patient go to the hospital as soon as possible for examination, and after the doctor clarifies the cause of the disease, targeted treatment will be given.