Pain under the tongue may be caused by the following three reasons: First, the more common mouth ulcers, if it is recurrent mouth ulcers, the location is not fixed, it is also likely to appear under the tongue. Secondly, it occurs in children, because the lower front teeth are sharp and the tongue tie of children is too short, frequent friction of the tongue tie can also form a kind of ulcer, which needs to be corrected by the doctor in time to the hospital. Third, eating too hot or too hard food, there is some trauma to the tongue body. If it is the third case, patients are advised to avoid eating too hot or too stimulating food during the trauma to avoid infection of the wound. Pain under the tongue is usually not a tumor or a cancerous lesion. If you find that the tongue gradually becomes hard, you need to go to the hospital as soon as possible to be examined and diagnosed by a doctor.