There is no specific clinical limit to how many hours a fever of 39℃ should last, but a fever of 39℃ is a medium to high fever, and it is recommended not to exceed 2 hours to avoid damage to brain cells. It is necessary to give warm towels to wipe the whole body and cold compresses to cool down the forehead, take oral acetaminophen, ibuprofen or aspirin and other antipyretics as prescribed by the doctor, and drink more warm saline to prevent dehydration caused by high fever. It is also recommended to seek medical attention in a timely manner to avoid damage to the organism and sequelae of high fever. If a child continues to have a fever of 39℃ for more than 2 hours, parents need to be alert to the occurrence of febrile convulsions, which are characterized by sudden onset of loss of consciousness, double vision, squinting or upturning, tonic or clonic convulsions of the head and limbs, respiratory pauses, facial bruises, etc. Most of the convulsions will soon recover, but if they continue to occur or recur, they indicate a serious condition. At this time, parents are advised to tilt the child’s head to the side to keep the airway open and avoid accidental aspiration of sputum that may block the airway and cause asphyxia. Do not press on the child’s body during the attack to avoid fractures. Promptly send the child to the doctor for treatment. Diazepam is often used for sedation and intravenous electrolyte infusion to maintain the physiological balance of the body. Early treatment is recommended for fever of 39°C. When the condition is under control, the body temperature will gradually drop within a short period of time, which is less damaging to the organism. If the fever is too long, it may lead to an accelerated heartbeat, thus damaging the heart muscle cells. If the body temperature rises gradually for a long time without intervention, it can lead to protein denaturation in the organism, causing irreversible cell damage and affecting brain function.