Generally, persistent high fever for 3-5 days can have a major impact on the body. Hyperthermia refers to a body temperature of 39°C or higher, and a persistent high fever that does not subside can produce many adverse reactions on the body. High fever will cause the body’s basal metabolism to increase significantly, resulting in a rapid heartbeat, shortness of breath, and muscle aches and pains throughout the body. At this time, if not timely hydration, the patient is likely to dehydration, leading to the occurrence of shock. Sustained high fever of 41℃-42℃ or more can cause great harm to the central nervous system, and often such damage is irreversible. In addition, persistent high fever can also affect the function of various organs in the body and may induce coronary heart disease and kidney damage. Therefore, it is important to seek medical attention in a timely manner once the fever persists for more than 3 days to avoid delaying the condition. Therefore, if a patient has a high fever that does not subside, the patient needs to seek medical attention, take rest, eat a light diet, and eat more protein-rich foods.