Cyanosis is a manifestation of cyanosis of the lips and mouth, cyanosis of the ends of the extremities, that is, the ends of the fingers of the hands and feet, and cyanosis of the skin. It is common in patients with chronic hypoxia, hypoxemia, long-term lung diseases such as chronic bronchitis, bronchial asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, or long-term smoking, all of whom suffer from long-term hypoxia, resulting in cyanosis of the ends of the extremities, lips, and other parts of the skin and lower skin temperature. If there is no cyanosis in the mouth and lips, but only cyanosis at the end of the extremities, lower skin temperature and purple skin, it indicates poor circulation at the end of the extremities and spasm of fine blood vessels and vascular capillaries, which is commonly seen in Raynaud’s syndrome.