Traditional Chinese medicine believes that nature and human body have six qi: wind, cold, heat, humidity, dryness and fire. Generally, it is called six qi. If there is excess of six qi, which is harmful to human body, it is six evils. Exogenous disease means that when the healthy qi of human body is insufficient, the six evils will take advantage of it and cause the human body to get sick, which is also exogenous disease.