How to Use a Thermometer to Check for Fever

If you think you or your child may have a fever, the best way to know for sure is to check your temperature (or your child's). If you do need to call the doctor, she will need to know how high your fever is. So, be sure you know how to check it the right way. After all, there are several different types of thermometers and it is easier to get it wrong than you may think.

Types of Thermometers

  • Oral - digital or manual
  • Rectal - digital or manual
  • Axillary - digital or manual
  • Tympanic - digital, checks the temperature in the ear
  • Temporal - digital, checks the temperature on the forehead

Checking the Temperature

If you are using a digital thermometer, simply press the button to turn it on.

  • Oral - Place under the tongue; Wait until the digital thermometer beeps or approximately 5 minutes for a manual thermometer; Remember not to take an oral temperature right after eating or drinking something because it will affect the results. It's also important to keep your mouth closed the entire time. Oral thermometers are not the best option for young children because they often cannot keep their mouths closed long enough to get a good reading.
  • Axillary - Place under the arm with the tip in the deepest crease; Wait until the digital thermometer beeps or approximately 5 minutes for a manual thermometer.
  • Rectal - Use lubrication, such as petroleum jelly and place tip in the rectum (opening in the bottom); Wait until the digital thermometer beeps or approximately 5 minutes for a manual thermometer; This method should be used for infants or those whose temperature cannot be taken any other way.
  • Tympanic - Pull the top of earlobe up and back, place tip (covered with probe cover) in ear canal opening, press button until it beeps; Be sure you are pointing the probe into the ear canal opening and not at the wall of the ear, this can result in incorrect results. Tympanic thermometers can be difficult to use on babies and are often inaccurate because their ear canals are so small. 
  • Temporal - Press button down and sweep probe across forehead; This is fairly new technology but seems to be relatively accurate and very quick and easy to use. Be sure to read the instructions for your device - some require a swipe across the forehead and on the neck below the ear. 

Mercury thermometers are no longer sold in the United States. They pose a danger if they break and release the mercury, which is toxic. If you have an old mercury thermometer that you decide to use, the mercury should be shaken down to below 96 degrees. Generally, they need to be held in place for about 5 minutes to get an accurate reading.

Do you need a thermometer? Can't decide which kind to get? Check your options.

  • Digital oral, axillary or rectal.
    • Digital thermometers are a great option. They are very inexpensive and much quicker and easier to use than manual mercury thermometers.
  • Tympanic ear thermometer.
    • These are very popular, especially among parents of small children. They are faster than regular digital thermometers and are easy to use. You should be careful to use it correctly and know that the results may not be accurate if the child has an ear infection.
  • Temporal scan thermometer.
    • The newest and most expensive thermometer on the market. These are the quickest (they only take 1-2 seconds) and probably the easiest to use. In my experience, they have been very accurate, but some people find they read too low at times.
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Article Sources

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  2. El-Radhi AS. Determining fever in children: the search for an ideal thermometerBritish Journal of Nursing. 2014;23(2):91-94. doi:10.12968/bjon.2014.23.2.91

  3. Mercury Thermometers. EPA. Published June 26, 2018.