Whether or not a mouth ulcer can heal itself in a day needs to be judged according to the individual’s situation, it may or may not heal itself. Clinically more common mouth ulcers are recurrent aphthous mouth ulcers or ulcers caused by trauma, may be self-healing, self-healing time varies from person to person, if the mouth ulcers are relatively mild, may be a day or so will be self-healing, but if the mouth ulcers are more serious, it may take 3 to 7 days or even more time. If mouth ulcers have developed, you need to pay attention to your personal diet, keep a light diet, you can also use medication under the guidance of a doctor, such as lidocaine gel, cedirizine tablets, chlorhexidine solution and so on. Usually need to pay more attention to rest, ensure sufficient sleep, enhance the resistance.