The oral cavity is the beginning of the digestive tract and the gateway to the respiratory tract. Some diseases of the oral cavity can cause other diseases, and certain systemic diseases can appear in the oral cavity with a variety of symptoms. The lip mucosa is thin, rich in blood vessels and nerves, and is the reaction window of the body’s blood pigment. If the blood pigment in a person’s body is normal, the lips are red, full and plump. Those with anemia have pale lips, and those with congenital heart disease and oxygen deficiency such as carbon monoxide poisoning have blue lips. Patients with hemophilia are prone to bleeding after intra-oral injury. In leukemia patients, the gums are enlarged, pale, edematous and prone to bleeding. Patients with lupus erythematosus have butterfly spot damage on the face and palate inside the mouth. Lead, mercury, and bismuth poisoning patients can have corresponding damage lines in the gingival part of the intraoral mucosa. Some oral lesions, repeated infection and inflammation can cause a variety of systemic diseases, such as rheumatic heart disease, arthritis, gastritis, rheumatic fever, iridocyclitis, etc. When the oral diseases are cured and the diseased teeth are extracted, certain diseases are not cured. Therefore, chronic lesions in the oral cavity should be treated early. People with periodontal disease have deepened gum pockets, often with pus and plaque formation, making teeth loose and fall off, which not only affects eating, but also can swallow pus into the stomach, leading to inflammation of the gastrointestinal tract. In short, oral diseases and systemic diseases can sometimes be causal and closely related to each other. To protect the health, it is necessary to conduct regular oral health examination for early detection, early diagnosis and early treatment.