Mouth ulcers are not pathologically related to constipation and are two different symptoms. The co-occurrence of mouth ulcers and constipation may be related to digestive system diseases, diabetes, premenstrual syndrome and other diseases. 1. Digestive system diseases: chronic gastroenteritis, irritable bowel syndrome, ulcerative colitis and other digestive system diseases can cause oral ulcers and constipation. In addition, the patient himself has constipation, the chances of suffering from mouth ulcers are also very high. 2. Diabetes: a metabolic disease that can lead to damage to autonomic nerve function and peripheral circulation, people who suffer from diabetes for a longer period of time may also experience oral ulcers and constipation. 3. Premenstrual Syndrome (PMS): refers to the repeated cyclical occurrence of emotional behavior and somatic disorders in women during the luteal phase, and PMS patients may experience oral ulcers, constipation, and other symptoms of somatic disorders. It is recommended that patients seek timely medical attention, improve the examination under the guidance of the doctor to clarify the diagnosis, and carry out targeted treatment.