There are several reasons for ulcers under the tongue: 1. The lack of vitamin B, vitamin C, trace elements or fire in the organism leads to redness, swelling and ulcers in the mucosa of the mouth. 2, 4.For elderly people who wear movable dentures in their jaws, the rough surface of the dentures or the rings of the dentures can scrape the sublingual mucosa and cause traumatic ulcers due to improperly made movable dentures. 5.If you eat spicy, stimulating, too hot, too hard food, it can also cause ulcers on the mucosa. 6.People who are in a state of tension and anxiety because of the fast pace of life, high work pressure or black and white The ulcers can also appear under the tongue of people who are upside down and stay up late.