The purple lips of diabetic patients may be caused by physiological factors, or it may be caused by coronary heart disease, lung infection and other diseases. 1. Physiological factors: the contraction of small arteries in the lips under the cold environment, heat dissipation is reduced, resulting in a decline in arterial blood flow through the lips caused by purple lips. 2. Lung infection: diabetic patients with poor blood sugar control are susceptible to various infections, when the body is infected by Streptococcus pneumoniae, Staphylococcus aureus and other pathogens can cause lung infections, which can cause lung ventilation or hyperventilation to decline, resulting in purple lips. 3. Coronary heart disease: diabetic patients with poor long-term blood sugar control can cause atherosclerosis, which leads to coronary heart disease, can cause blood vessel lumen stenosis or occlusion, which leads to hypoxia, ischemia, purple lips. It is recommended to go to the hospital when the phenomenon of purple lips occurs.