First, the reason for cold hands and feet is related to the body's response to the drop in ambient temperature. When the ambient temperature drops, in order to avoid the temperature drop, the skin "cold receptor" will send information to the brain temperature regulation center, which will increase the muscle tension of the body by exciting the sympathetic nervous system, causing "trembling" and increasing the generation of heat energy in the body. "Trembling with cold" is the truth. Tremor can increase the heat energy generated by the body from 40 to 60 kilocalories per hour to 300 kilocalories, contract the blood vessels on the body surface, and reduce the heat energy loss of the body to keep warm. In addition, when it is cold, most people stay indoors, and the sun and exercise are reduced. In winter, the platelet and coagulation function in blood are stronger than in summer. In addition, it is easy to cause respiratory tract infection in winter, which increases blood viscosity and coagulation function, leads to poor blood circulation and aggravates cold hands and feet. Second, even healthy people may have cold purple hands and feet in cold weather. Sympathetic nerve excitation will cause arterial blood vessels to contract, microvessels and venous blood vessels to expand relatively, and the oxygen content in tissues will decrease, so the skin will be blue-purple for a period of time, extending from fingertips to palms. Light pressure will not turn white, more common in women under 30. Sometimes there will be a "reticular green spot" change, and some skin will have mottled red and blue reticular fine lines, which may occur in women or men around the age of 30. Most of these skin changes are harmless and can be improved by keeping warm, but sometimes they also occur in the skin with acute arterial embolism. There is also a skin change called "Raynaud's syndrome", which occurs in women aged 20 to 40. There is a periodic color change of fingers or toes "from white to purple, then to red". Most of them occur in fingers, with only one or two fingers (toes) at first, and then gradually spread to other fingers (toes). A few people even reach the earlobe and the tip of the nose, and most of them are fine. As long as they pay attention to keep warm and avoid exposure to cold environment, about 15% will get better with time, but 30% will get worse gradually, less than 30%. Less than 1% of fingers will be amputated due to severe ischemia. 3. When should I see a doctor to check the cold hands and feet and the change of skin color caused by cold? As long as there is no pain, normal pulse, no wound on the skin, and normal skin color or oral mucosa color in other parts of the body, most of them are not serious. Arterial diseases caused by arterial spasm or other diseases often cause changes in the skin of hypoxic affected areas: pale, smooth and bright skin, sparse hair and thickened nails; In severe cases, the skin is purple-black, with pain, ulcer, gangrene and even amputation. Therefore, if the cold hands and feet are accompanied by abnormal pain, numbness, weak pulse or disappearance, and the above skin lesions appear, and patients with Raynaud's syndrome have frequent or aggravated attacks, they should seek medical examination. If other major medical diseases are known, such as hypertension, heart disease, diabetes, autoimmune diseases, arterial diseases, etc. They should see a doctor as soon as possible. In addition, we should also note that many drugs can also cause arterial vasoconstriction.