4 Mistakes People Make When Using a ThermometerPart 3 in our series on fever

by James Hubbard, MD, MPH

Think you know everything about how to use a thermometer correctly? If you read this post until the end, I’ll wager you’ll learn something you didn’t know. And understanding the right way to use a thermometer is important for various reasons.

When people bring their child to my office because of fever, one thing I ask is if they’ve actually taken their temperature with a thermometer. Many have not. Either they don’t have one or they’re not sure they can use a thermometer correctly.

Even if you’re in a situation where you can’t get to a doctor, exact readings taken at different times of the day can be an important clue in making a proper diagnosis. With many infections—strep throat is one I see a lot—the fever is usually a lot lower in the morning than it is in the evening. Also, knowing if your fever is lower today than it was yesterday can be an objective sign you’re getting better. Of course, if it’s not, or if it’s higher, that may be an indicator of the opposite.

If you don’t have a thermometer, I suggest you get one the next time you’re out. Get the digital kind. It’s easy to use (a beep goes off to tell you it’s time to remove it), and it’s more reliable than the skin or ear kind. In fact, buy an extra one for your bug-out bag. If you’re concerned the battery might go dead, a good alternative is an alcohol-based bulb one that you keep in a safe place so it won’t break.

How to Use a Thermometer: 4 Mistakes People Make
How to Use a Thermometer With Kids

Q. Can I use a skin or ear thermometer?

A. If you just want to know if the child is running a fever and you’re not too worried about exactly how much, or if taking the temperature is going to be a big ordeal, you can use the skin or ear thermometer. Or you can place an oral bulb thermometer under the arm for about five minutes (or, if it’s digital, until it beeps). Keep it in place by holding the child’s elbow next to the body. If there’s fever, you can then take a more accurate oral or rectal reading.

Q. How (and why) would I take a rectal temperature?

A. A rectal temperature is the most accurate and is the way you’ll measure the temperature of young children who can’t hold a thermometer under their tongue. Turn the baby face down, apply a lubricant to the tip, and insert the tip about a half-inch. Keep in place for one to two minutes. A good way to hold it in is to place your palm on the buttocks and hold the thermometer lightly between your index and middle fingers.

For a rectal temperature, you use the same type of thermometer as you would use in your mouth, so be sure to label it so you don’t get it mixed up and use it in your mouth next time.

1. They don’t wait at least 15 minutes after eating or drinking to put the thermometer in their mouths.

2. They don’t keep it in long enough. If you have a digital kind, just follow the directions. For the bulb type, keep it in under your tongue for a couple of minutes.

3. They compare temperatures taken at different times of the day, not realizing that even in people who are not sick, temperatures vary from morning to evening. As I’ve already mentioned, they can do this even more depending on what’s causing the fever. So don’t compare yesterday morning’s temperature to the one you take this evening. Rather compare the one you took around 9 a.m. yesterday to the one you take today around that time.

I’d suggest taking the temperature mid-morning, mid-afternoon, and at night. Write the findings and times down. Then take them at approximately the same times the following day to monitor improvement or worsening.

4. They don’t use a thermometer. Instead, they rely on how they feel or how the skin feels.

Some people ache and feel really bad with a temperature of 99. Others feel pretty good with a fever of 101. How you feel is not necessarily an indicator of whether you have a fever.

How your skin feels isn’t a good indicator either. Many people think they’re running a fever because their skin feels hot. Of course that may be the case, but skin can be flushed for many reasons.

Think about it. All it takes for someone’s skin to feel hot is your hand being cooler than the skin you’re touching. And our skin surface temperature varies throughout the day.

Try cooling off your hand under a faucet. Dry it and touch your forehead. You’ll get the idea.


What’s been your experience with thermometers? Which type do you use? Have you taken your temperature only to find it normal when you think it would be high, or vice versa?

The fever series so far: