A black and purple blood blister on the inner wall of the mouth may be caused by mechanical irritation and thermal irritation. It is recommended to remove the irritation, pay attention to the care of life and diet, and consider surgical treatment if necessary. 1. Mechanical stimulation: sharp tooth tip, residual crowns and roots, rough tartar, blocked wisdom teeth, causing adverse local stimulation, resulting in capillary rupture and formation of blood blisters. It is recommended to go to the hospital stomatology department for examination to prevent the recurrence of blood blisters by removing the mechanical stimulation. 2. Thermal stimulation: Intake of hot food, resulting in damage to the oral mucosa, capillary rupture can form blood blisters. It is recommended to pay attention to diet, avoid eating too hot, spicy stimulating food. With the passage of time, blood blisters can be absorbed on their own. The appearance of a purple-black blood bubble on the inner wall of the mouth, it is recommended to go to the hospital stomatology department for examination, first to clarify the cause, and then for the cause of the treatment.