Darkened lips are often indicative of heart or lung disease. The most common heart diseases are congenital heart defects, such as large atrial septal defects, ventricular septal defects, arterial duct failure, and tetralogy of Fallot. Such diseases can cause a left-right shunt of blood in the heart, resulting in the flow of blood from the right atrium into the left cardiac system, i.e., venous blood mixing with arterial blood, which can lead to a decrease in the oxygen content of the circulation, resulting in bruising, or cyanosis, and also darkening of the lips, and severe cardiac insufficiency can lead to the appearance of the above symptoms. Long-term chronic lung disease can also cause the above symptoms, such as chronic bronchitis, chronic obstructive pulmonary disease, chronic bronchial asthma, etc., can also cause a drop in blood oxygen, resulting in black lips.