Fever caused by a bacterial infection usually lasts about 7 days, and fever caused by a viral infection may last 3 to 5 days. In mixed infections, the fever may last longer. 1. Bacterial infection: After bacterial infection, the toxins and metabolites produced by the bacteria can be used as a thermogenic source to stimulate the thermoregulatory center to cause fever, which usually lasts for about seven days. However, if the body’s immunity is low, or the bacterial virulence is too strong to cause bacteremia or sepsis, the fever will last longer. 2. Viral infections: Viral infections usually inhibit the function of the body’s cells and may even damage the cells. The fever caused by viral infection is usually low and lasts for about 3~5 days, then most of the fever can subside by itself. 3. Mixed infection: If bacteria and virus infect the body at the same time, it may cause more serious symptoms. If the immune system is weak, the fever may last longer, up to 7~10 days. Whether it is bacterial infection or viral infection, if the symptoms of cough and fever last for more than 3 days and continue to be unrelieved, or are accompanied by other uncomfortable symptoms, it is recommended to go to the hospital in time.