When to Worry About a Fever

Do you starve or feed a fever? Can fever cause brain damage or seizures? Find out the truth from House Call Doctor

Rob Lamberts, MD,
January 17, 2013
Episode #022

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When to Worry About a Fever

Having practiced medicine for over fifteen years, I have taken care of a whole lot of people, and some of them have been really hot. Before my wife starts to worry, I am not talking about metaphorical hotness; these people were literally hot. 

What is a Normal Body Temperature? 

If you haven’t guessed it, this post covers the topic of fever and when to worry about one. Fever, of course, is a condition when the body temperature is higher than normal. I bet you knew that. But it’s not as simple as you think.

When discussing fever, the first question we have to answer is: what is a normal body temperature? At first blush, that may seem straightforward: a temperature above 98.6F is normal. Unfortunately, there are a number of things that make this a bit more complicated.

First, there are a lot of ways to take a temperature. A person’s “true” temperature is defined as their core temperaturethe temperature deep inside the body. The body temperature in the arms, legs, and on the skin can be substantially different from the core temperature. So to accurately know the body temperature, a core temperature is best.

The problem is that it is both impractical and dangerous to stick a probe into someone’s liver to check the core temperature, so other more reasonable means have been invented, each with its own strengths and drawbacks. These include:

  • Oral temperature, which most of the time gives an accurate estimate of the core temperature, but can vary depending on a person’s cooperation and other factors.
  • Axillary temperature, which is the temperature under the arm. This is the easiest to take, but is also the least accurate.

  • Rectal temperature is the most reliable, but the least popular among patients.

  • Other devices such as ear thermometers and heat-sensitive strips that can be placed on the forehead are inaccurate, but quite easy to use.