A baby’s fever usually goes down in about three to seven days, depending on the cause and degree of the illness that occurs, etc., and no generalizations can be made. 1. Upper respiratory tract infection: If it is a common viral infection caused by upper respiratory tract infection, which leads to the baby’s fever, usually lasts 3-5 days will slowly get better. Some babies with lower immunity, the fever will last longer, may last 5-7 days, parents are advised to choose the way to lower the temperature according to the baby’s temperature. 2. Lung inflammation: due to lung inflammation caused by fever, it is recommended to take anti-inflammatory drugs or fever-reducing drugs under the guidance of a doctor to treat the mild symptoms may soon be able to reduce the fever, some may need a week or so to reduce the fever, but the serious ones may take about 2-3 weeks or even longer to reduce the fever. There may be other reasons for your baby’s fever, with different causes, different degrees, different treatments and different times to reduce the fever. It is recommended to go to the hospital, the doctor according to the condition, and then give the relative treatment.