Some people have fine blood vessels, and some people have a weak constitution, such as a small amount of blood circulation, and they have fine blood vessels. A good number of female patients have finer blood vessels, and male patients have fuller blood vessels. When female patients have menstruation, they have less blood volume in their bodies and their blood vessels are correspondingly thin. In some female patients, although there is no diagnosed disease, the blood flow is slow, some of which is physiological and not pathological. When the arterial blood vessels are felt to be thin, the lower extremity feet may feel cool and cold, and there will be a fear of cold. It may be necessary to go to the hospital to check the arterial ultrasound of the lower extremity to observe if the blood vessels are slow flowing and thin, etc., while some people with small body size will have thinner blood vessels.