Humans are warm-blooded animals. No matter how much the outside temperature changes, the body temperature can be maintained at around 36-37℃ under normal circumstances through the regulation of the hypothalamic temperature regulation center. However, the human body has a certain tolerance limit to the degree and duration of the increase in the ambient temperature. If the body is exposed to high temperature for a long time, the body will lose its regulatory compensatory function. When the body temperature regulation function is disturbed in a high temperature and high humidity environment or under direct sunlight for too long, it causes a series of symptoms such as water and electrolyte metabolism disorders and damage to the nervous system. This is heat illness or summer fever. Generally, those with an acute onset and a more serious condition are called heat stroke. Those with a slow onset, milder symptoms and a longer duration are called summer fever. In recent years, due to the improvement of living standards and the extensive use of air conditioners, its incidence has shown a clear downward trend.