The gums are black due to pigmentation, poor blood circulation, gingivitis, as follows: 1, pigmentation of patients are caused by smoking, due to long-term smoking where the pigmentation, soot will gather on the surface of the gums, if not regularly cleaned or brushed on time, the pigment will slowly accumulate and settle on the surface of the teeth resulting in black, and difficult to remove. 2, due to excessive intake of heavy metals, such as lead, mercury 3, due to damage to the dental nerve or the stimulation of gingivitis, resulting in inflammation and congestion of the gums, when the inflammation is eliminated, the original swollen, congested red pigment will slowly settle and eventually become black. So if gingivitis attacks often, the gums are gradually darkened, so it is important to actively prevent and treat gingivitis, and it is recommended to go to the dentist regularly for the appropriate examination, early detection and early treatment of dental disease.