There are more causes of black lips. Lack of vitamin C in the usual diet can easily cause dark lips. Problems with the digestive system, such as constipation, diarrhea, indigestion, etc., can easily cause dark lips. Patients suffering from renal insufficiency or kidney failure will have dark lips. Patients with chronic hepatitis B, with the gradual aggravation of the disease, liver function is impaired, and the deterioration of the disease will also appear black lips. There are also some patients with chronic obstructive pulmonary disease, due to respiratory difficulties caused by lack of oxygen in the blood, will appear black lips. If the symptoms of black lips appear, you need to go to the hospital to see an internist in time to do specific tests to confirm what causes it and treat the cause in time.