A blood blister on the tongue that hurts when it rots can be caused by traumatic blood blisters, herpes simplex or oral ulcers. 1. traumatic blood blisters, if the external stimulation caused by tissue fluid oozing, there may be a blood blister on the tongue after rotting very painful symptoms, usually do not need to use drugs to treat, may be a few days after the recovery. 2. Herpes simplex, if there has been a herpes simplex virus infection, herpes virus invasion may lead to this symptom, you can use acyclovir, vasiclovir and other medications under the guidance of a doctor, to promote the rapid healing of blood blisters. 3. Oral ulcers, if the blood blisters are caused by oral ulcers, you can use watermelon cream, cidiarotene iodine and other medications to avoid aggravation of the symptoms. Usually need to pay attention to personal oral hygiene, if there is obvious discomfort, it is best to consult a doctor in time.