The main reasons for the appearance of purple lips are the following: 1, lung causes: common in chronic bronchitis, obstructive emphysema, these lung diseases can cause the blood contains less hemoglobin, or hemoglobin carries less oxygen, causing the skin and mucous membrane ischemia and appear purple lips. 2, heart causes: mainly manifested as heart failure, and coronary heart disease, congenital heart disease and 3. Nitrite poisoning: If you take too much food containing nitrite, such as pickles, sauerkraut, etc., you will experience cyanosis caused by food.