Your baby has a fever of 40 degrees, and this is a high fever. And high fever can easily cause febrile convulsions in children, so it needs to be dealt with as soon as possible. Measure the temperature of 40 degrees, first give the child to take antipyretic drugs, commonly used are ibuprofen suspension, also known as Merlin, acetaminophen, also known as Tylenol. After giving the child with antipyretic drugs, it is necessary to give the child more water, only after replenishing sufficient water, in order to make the antipyretic drugs work, the baby sweating body temperature can slowly fall. After this treatment, if the body temperature slowly decreases and the baby is in good spirits, you can temporarily observe at home. Physical cooling methods such as warm water scrubs or ice patches are not recommended at this time because they may cause discomfort to the child. If your baby is not in good spirits, you need to take your child to the hospital immediately. Generally, after going to the hospital, you need to conduct a routine physical examination of your child, and then take blood tests to determine whether your child has a bacterial or viral infection, and then actively treat the symptoms. If the child continues to have a fever of forty degrees that does not subside, and general respiratory infections are ruled out, he or she needs to be hospitalized and undergo a whole-body examination according to the fever pending investigation. A high fever of forty degrees requires immediate treatment, active use of antipyretic drugs, more hydration, good rest, and active identification of the cause of the fever for etiological treatment is very important.