Yang deficiency is the name of a disease. It refers to the symptoms of insufficient Yang Qi or functional decline. "Suwen·Tiaojing Lunpian" says: "Yang deficiency leads to external cold." It usually refers to Qi deficiency or Mingmen fire decline, because Qi and Mingmen are both Yang, hence the name. The lung governs Qi, and Qi deficiency mostly refers to lung Qi deficiency or insufficient Zhong Qi, so the Wei surface is not solid, so it is externally cold; Yang deficiency leads to Yin excess, so Mingmen fire decline is also often seen in functional decline and turbid Yin accumulation. In addition, Yang deficiency can also be seen in heart Yang deficiency or spleen Yang deficiency. Symptoms include pale complexion, cold hands and feet, fear of cold, easy sweating, loose stools, clear and long urine, pale lips, tasteless mouth, loss of appetite, pale tongue, white and moist fur, weak pulse, etc. Treatment should be warm and tonifying Yang Qi.