Colds are caused by external influenza. People with liver and kidney yin deficiency (insufficient yin in the liver and kidneys) are more susceptible to external influenza due to the deficiency of positive qi and the lack of solidity of the guards, which is an internal cause of colds. Colds can be caused by wind, cold, summer, dampness, dryness and other six kinds of diseases or seasonal viruses, and the key to whether or not a disease develops after an attack on the human body by an external evil lies in the strength of the guardian qi and the severity of the evil. The key to the onset of the disease is the strength of the Wei Qi and the severity of the evil, and those who have a weak body are often difficult to recover from the external evil, which is called a deficiency cold. Cold and flu can be categorized into qi deficiency and yin deficiency, while those with liver and kidney yin deficiency have insufficient yin and blood, weakened guard function, and are susceptible to attack by external evils, resulting in a loss of harmony of the guard, which in turn leads to cold and flu, which is the internal cause of cold and flu. It is recommended that people with liver/kidney/yin deficiency who also have colds should consult regular hospitals and be treated by professional doctors.