by Rob Lamberts, M.D.
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.
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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 temperature--the 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.
The oral temperature generally runs 1 degree and the axillary 2 degrees below the rectal temperature.
Another complicating fact is that a person’s body temperature varies, with a fluctuation on any given day by as much as half a degree. Menstruating women’s temperatures vary significantly depending on where they are in their cycle.
The bottom line is that the measurement of a person’s temperature can be quite inaccurate, and should be interpreted in such a way.
What is a Fever?
So what is a fever? The standard definition is that a fever is a rectal temperature above 100.4 F. A fever is caused by the body itself--usually in response to an infection--when the thermostat in the brain purposely raises the body temperature. There are other causes of fever, including systemic diseases, cancers, and staying out in the heat too long, but I’ll just cover the infectious cause in this podcast.
Is a Fever Good or Bad?
So, is fever bad? No, fever is the response of the body to fight off infection. Let me say that again: fever is a good thing. Here are the ways in which fever is good:
It tells us when there is an infection, and the pattern of fever may give clues to the type of infection
It slows us down so our bodies can focus on fighting the infection while we lie pathetically in bed
Many infectious organisms don’t grow as well when the temperature is raised
There is evidence that the immune system works better when a person has fever
Can Fever be Harmful?
So what about the belief that fever can cause brain damage? It’s a myth that creates an unhealthy fear about fever. Only brains that are already damaged or brains overheated from the outside are at risk of being damaged. A person with a fever accompanying an infection will not get brain damage, no matter how high the temperature.
The fever itself is not harmful, but the infection that causes it may be.
But that does not mean you should never worry about a fever. Fevers are a clue that may tell us that the person has a dangerous infection. The fever itself is not harmful, but the infection that causes it may be.
When to Worry About a Fever?
So when is it OK to worry about a fever? A fever in an infant under four months of age should always cause concern and the baby should be seen immediately. Young infants can have serious infections with the only sign being a fever. Only the trained eye can determine whether to worry or not, and infants under two months of age are often hospitalized with only a fever, just to be on the safe side.
In everyone else, the symptoms that accompany the fever have to be taken into account in deciding when to worry. A fever and stiff neck may mean meningitis. A fever with cough and difficulty breathing may mean pneumonia. In all of these cases, fever is just a part of the puzzle pointing to the underlying disease.
Finally, a fever that lasts over a week can be the sign of something more serious. Most fevers lasting this long are not serious, but they should prompt a visit to the doctor.
How Should You Treat a Fever?
When I was training to be a pediatrician, I often gave the “fever is your friend” lecture, encouraging parents to not treat their children’s fevers. Then I had children and saw just how awful they looked. It’s hard for a parent, even if he is a pediatrician, to stand by and do nothing in this circumstance.
This highlights the main reason to treat a fever, which is for comfort. People feel lousy when they have a fever, and treating it makes them feel better. Though fever does have its benefits, those benefits are not huge, so treating fever with acetaminophen or ibuprofen is perfectly acceptable. There is no medical benefit to the person to treat the fever, but it is certainly OK to want to feel better.
An exception to this is the child under 4 months of age. They should be evaluated first before treating the fever.
Quick and Dirty Tips
So here are my quick and dirty tips about fever:
Tip 1: Don’t freak out – Yes, fever makes you feel lousy, but it doesn’t need to be treated. It won’t hurt you.
Tip 2: Know when to worry – Fever in children under four months of age, fever along with other serious symptoms, and fever lasting over a week are all reasons to seek medical attention.
Tip 3: Know how to take a temperature – Infants should always have temperatures taken rectally. That is really the only time when knowing the exact temperature is crucial. All others can be taken however is most convenient. Our office uses oral thermometers except on infants.
Tip 4: Report temperature properly – Don’t add or subtract degrees when you report the temperature. Just say what the temperature was and how you took it.
Tip 5: Know how to treat fever – Using acetaminophen and ibuprofen is generally safe and effective. I don’t advocate using warm baths, as they could induce shivering, which raises the temperature.
Tip 6: Trust instinct – You still can be sick without a fever. If you are worried you or your child may be seriously ill, get in to be seen immediately, even if there is no fever.
If you have questions you want answered, send them to email@example.com. You can find me on Twitter as @housecalldoc and on Facebook under “House Call Doctor.”
Disclaimer: Let me remind you that this article is for informational purposes only. My goal is to add to your medical knowledge and translate some of the weird medical stuff you hear, so when you do go to your doctor, your visits will be more fruitful. I don’t intend to replace your doctor; he or she is the one you should always consult about your own medical condition.
Catch you next time! Stay Healthy!