Colonoscopies and gastroscopies are generally harmless, but there is a low chance of injury for a variety of reasons. Gastroscopy may cause damage to the mucous membranes of the mouth or other parts of the body, but such symptoms are relatively mild and can be healed quickly. In some patients with gastric ulcers, bleeding or even perforation of the ulcer site may occur during gastroscopy, which is a more serious but less common condition. Occasionally, colonoscopy may cause damage to the mucous membrane or a small amount of blood seepage, but this symptom is relatively mild and can be healed quickly. Injury to the intestines, such as bleeding or even perforation of the intestines, is also possible and is more serious, but can usually be resolved endoscopically and is less common. If a patient needs to have a gastroscopy or colonoscopy, he or she should explain clearly to the doctor about his or her current and past medical history, and cooperate with the doctor’s operation in order to minimize the damage caused by the operation to the organism.