Many diseases can cause fever for several days in a row, such as some viral infections. There are also some common infectious diseases in infants and children, such as early childhood emergencies, rubella and chickenpox, because the course of the disease takes a few days. If the disease progresses under normal circumstances, with symptomatic treatment, the patient will also appear to recover, so there is no danger. Fever is an increase in body temperature above the normal body temperature. Fever accompanies the onset of the disease and may last for a certain period of time. With timely medication, the disease progresses smoothly and the fever symptoms improve. For example, urinary tract infections and purulent tonsillitis are associated with recurrent high fever. As long as the infection is controlled with active anti-inflammatory treatment, the body temperature will return to normal. However, for some patients with high fever, if the cause is not identified and treatment is delayed, the fever will persist and will affect various organs and tissues of the body, especially the brain, which is the most damaging, and if the body temperature is greater than 40-41°C, it will cause cerebral edema and changes in consciousness. Whether a fever lasting several days is serious or not depends on the type of disease the patient is suffering from and whether the treatment is timely and correct. In short, regardless of the disease, if a fever persists, it is important to go to the hospital to identify the cause and then treat the cause and symptoms to avoid delaying the disease.