The duration of fever caused by different diseases is not the same, usually the fever should not exceed 3 days when observed at home, more than 3 days should promptly go to the hospital for treatment. There are many kinds of diseases that cause fever. For fever caused by upper respiratory tract infection, it can be observed at home and expected to heal itself, and usually the body temperature can return to normal in 72 hours. If the body temperature still does not subside in 72 hours, depression and severe respiratory symptoms, it is necessary to be alert to the emergence of complications or caused by other diseases, and should be actively examined at the hospital. In addition, many diseases can cause prolonged fever, such as tuberculosis, which manifests as prolonged low-grade fever; leukemia and lymphoma, which can manifest as repeated fever; cancer and burns can cause fever, so there is no strict meaning of fever time. During the fever period, attention should be paid to drinking more water, resting more, and eating a light and easily digestible diet. If the fever persists without remission or even worsens, it is important to seek prompt medical attention, and then actively treat the fever after a clear diagnosis.