What causes lips to blacken?

Lip blackening, first of all, is caused by local pigmentation, and chronic kidney failure and other chronic diseases, resulting in long-term accumulation of toxins in the human body, skin mucosa melanin hyperpigmentation has a great relationship; secondly, it is considered that enteritis, chronic gastritis and other digestive system diseases are more likely, in addition to the symptoms of lip blackening, abdominal distension, diarrhea, decreased appetite and constipation, etc.; In addition, it cannot be ruled out that vitamin C deficiency in the body and the possibility of acute syphilis, pulmonary heart disease, etc.