Pain on both sides of the mouth is considered to be caused by diseases such as oral ulcers, xerostomia, mumps and periodontitis. 1. Mouth ulcers: the cause of the disease is not clear, may be related to genetic factors, decreased immunity, improper diet and so on. When patients have mouth ulcers on both sides of the mouth, pain, swelling and other uncomfortable symptoms may occur due to local mucosal damage. 2. Keratitis: Keratitis can be caused by pathogenic microbial infections, trauma, lack of nutrients and so on. The patient’s lesion will be accompanied by dryness and tightness, slight burning sensation, pain in opening the mouth, localized thickening of the skin and mucous membrane, which may be manifested as pain on both sides of the mouth. 3. Mumps: Mumps is mainly caused by infection with the mumps virus and is contagious. Mumps often causes parotid gland enlargement, swelling and pain in the parotid area, difficulty in swallowing and other symptoms, which may also manifest as pain on both sides of the mouth. 4. Periodontitis: Periodontitis can also cause pain on both sides of the mouth in some patients, and it is easy to be accompanied by other symptoms such as red and swollen gums and loose teeth. The occurrence of periodontitis is related to food impaction, plaque and calculus deposition. There are many causes of pain on both sides of the mouth, such as gingivitis, jaw joint dysfunction and so on. It is recommended that the patient consult a doctor for examination, clear the cause of the disease and then follow the doctor’s instructions for treatment, do not use drugs indiscriminately.