There is no specific requirement or rule on how long a child’s fever of 40 degrees should not exceed 40 degrees, but when the fever is 40 degrees, you need to go to the hospital as soon as possible to get rid of the fever as soon as possible. Usually, there is no strict requirement on how long a child’s fever of 40 degrees should not exceed 40 degrees. However, a persistent fever of 40 degrees is somewhat dangerous. When the fever is 40 degrees, due to the child’s nervous system development is not perfect, easy to cause febrile convulsions, prolonged convulsions may cause irreversible damage to brain cells. In addition, if a child with a fever of 40 degrees can easily lead to a lack of water in the body, if not replenished in a timely manner, it is likely to cause dehydration, and in severe cases, it may also induce brain cell edema or necrosis, the central nervous system has a certain degree of harm. When a child has a fever of 40 degrees, you need to go to a regular hospital within the first hour, and follow the doctor’s instructions to actively treat.