Does a fever raise temperature equally?

19 May 2015

Question

Does a fever raise temperature equally over the entire body? When a person runs a fever, will sometimes their head warm more than their chest?  What about the temperature of body parts that are less involved in symptoms, like the trunk, pelvis, legs and arms?  Will their temperatures rise equally?

Answer

We put Joe's question to Chris Smith... Chris - Well, first of all, why do you run a fever? You run a fever because some chemical is being produced in your body that triggers your brain's temperature regulating centre called your hypothalamus to turn up the thermostat. Why does this happen? Well, it can happen usually because you have an infection. When microorganisms cause inflammation, they damage tissues. They release various inflammatory chemicals and also, particles from the surfaces of the microorganism, the bacteria for instance have chemicals called lipopolysaccharide, LPS, which is part of the wall of the bacterium. This triggers your hypothalamus to sense that there is an infection and it turns up the set point for your body temperature and this triggers the release of more thyroxin which increases your metabolic rate and that makes you hotter, more adrenalin which increases your metabolic rate and that makes you hotter, it vasoconstricts you so you move blood more towards the centre of your body, slowing down the rate at which you lose heat, and that puts your temperature up. There are other reasons why you might run a temperature, but those are the most common reasons. That means that your core body temperature will go up and usually, it can go up from a normal of about 37 degrees to perhaps 40. The highest ever recorded temperature in a human being actually was 45 degrees and they survived. It was pretty impressive. But most people don't go much beyond 40. The body does this because when you increase temperature, you make it harder for infecting microorganisms to grow. you make it easier for your white blood cells to move around, and you therefore frustrate the bug and benefit the body. So, it's a sort of defensive mechanism but it won't happen equally everywhere for the simple reason that you're shunting blood towards your core so the core will be warmer, but your peripheries may actually be shut down and cooler. But there will be a global increase in body temperature right across your body when you're running a temperature. So, if you put your hand on someone's forehead, yes, it's going to feel warmer. But the best way of measuring temperature to get the core temperature and that's the thermometer actually in your bottom.

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