Black gums like bruises may be caused by smoking, or gingivitis, mercury poisoning and other diseases. 1. Smoking: If you usually smoke often, teeth for a long time in the tobacco burning rendering will appear brownish black or dark gray pigmentation. 2. Gingivitis: the disease is caused by dental plaque and is related to open mouth breathing, misaligned and crowded teeth, food impaction, bad restorations and other factors. Bleeding gums is a typical symptom of this disease, some patients with severe inflammation of the gums will appear on the black pigment attachment, can be manifested as black gums like bruises. 3. Mercury poisoning: this disease is caused by long-term inhalation of mercury vapor or mercury compound dust, accidental intake of mercury agents, and mercury vapor leakage, poor ventilation of the working environment, high temperature and other factors. Typical symptoms are swollen gums and the presence of blue-black mercury threads, so the patient’s gums are blackened like bruises. When there is black gums like bruises, you need to go to the hospital in time to clarify the specific cause.