The causes of fever in children that are hot at one time and not at another include the following: First, the situation caused by the child’s condition in the application of antipyretic drugs. When a child has a fever, parents or doctors will apply antipyretic drugs such as acetaminophen or ibuprofen to the child, and after the antipyretic drug is given to the child, the effect of the drug can be maintained for 4-6 hours. After the effect of the antipyretic drugs has worn off, the fever will recur again. Secondly, it is caused by the ups and downs of viraemia. When a child has a viral infection with a fever, the viremia will rise and fall in waves, causing a bout of fever. This is when the viral infection attacks the child’s blood circulation, causing viremia, which fluctuates in waves and causes the fever to recur.