Fever is not all bad. In fact, raising your body temperature enhances the body’s infection-fighting defenses. Lizards, fish and even cockroaches and leeches mount a fever to fight infection. But only humans take medicine to get rid of their fever.
If fever blocks the multiplication process of germs and enhances immune system function, what happens when we block fever? Researchers at Kings College London considered this question and wondered whether treating fever will actually make an illness last longer. In their review, published in September 2013, the British researchers reviewed 5 studies that evaluated whether taking anti-fever medicine slowed recovery from an illness. While there were limitations to these studies, taken together they suggest that treating a fever does not prolong an illness. Which only proves to me what I have suspected all along; fever is going to do whatever it wants.
Parents tell me all the time that they have given their child medicine for a fever, and it worked initially. But then they are shocked to discover that “the fever came back!” And that’s when they become concerned. I explain that a fever will come and go over the course of days in order to fight off an infection, and when the infection is gone, the fever will go away, but not until it’s good and ready. So, now I finally have some concrete evidence behind my advice. The truth is that we don’t have much control over fever or the course of an illness. All we can do is try to make children feel as comfortable as possible by giving fever medications and lots of fluids to drink until they get better on their own.
To take it even further, fever literally has a mind of its own. Fever is controlled by the hypothalamus in the brain, which is the thermostat of the body.
Substances called pyrogens cause fever. Some pyrogens are the waste products from viruses or bacteria, and some are made from the body’s own immune system trying to fight a germy invader. Pyrogens float around in the body during an infection. They don’t actually enter the brain, but trigger a chemical messenger that goes to the brain, which changes the temperature “set point” in the hypothalamus. The brain then begins to raise the body temperature because it thinks that the temperature is too low, like when your heater comes on after you turn up the thermostat. A child will shiver to create heat and close off the blood vessels in their hands and feet in order to increase the temperature in the center part of the body. So a shivering, clammy child is going to look quite ill.
During this process, a child will feel cold (and have the “chills”) because their actual temperature is below where the brain thinks it should be. Once the temperature of the body gets to the new set point, say 103 degrees, the child might actually feel more comfortable and stop shivering.
Later, when you give a fever-reducing medication, the medication works by turning the set point in the hypothalamus down. The child’s body temperature will be warmer than where the set point is and they will feel the sensation of being too hot. In order to cool the body back down to the new set point, a child will begin to sweat and their blood vessels will open up to release heat, which will make the child appear flushed.
So that’s why kids look so crappy when they have a fever, and as soon as you get to the doctors office or ER, they look great. Don’t worry they will look sad and icky as soon as you get back home. And remember, a fever is like an unwanted houseguest; it’s not going to go away until its good and ready.
 Does the Use of Antipyretics in Children Who Have Acute Infections Prolong Febrile Illness? A Systematic Review and Meta-Analysis. Purssell E, While A. J Pediatr 2013;163:822-7).