Sudden swelling of the mouth may be due to allergies, chronic lipitis, herpes of the mouth and lips and other diseases. 1. Allergy: this disease occurs because of contact with allergens caused by the body’s immune system abnormal reaction caused by genetic, cesarean section children and other factors related to common allergens such as peanuts, wheat, milk, eggs, lipstick and so on. Typical symptoms are edema in the mouth, lips, face and other parts of the body, so patients will have a sudden swelling of the mouth. 2. Chronic lipitis: the cause of this disease is not clear, research has shown that it may be related to dry climate, wind, cold and other environmental stimuli, followed by addiction to tobacco and alcohol, lip licking, lip biting and other bad habits, as well as irritability, anxiety and other mental factors. The patient’s lips will appear flaking, swelling, burning, pain, itching and other symptoms. 3. herpes orofacialis: the disease is mainly caused by herpes simplex virus infection, can be transmitted through direct or indirect contact, can be induced by stress, trauma, wind and sun exposure and other factors, and then there will be a sudden swelling of the mouth, but also fever, malaise, anorexia and other symptoms. It is recommended that patients with sudden swelling of the mouth go to the hospital, complete the relevant examination to clarify the specific cause.