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Taking a Temperature with a Digital Thermometer

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Fever is a symptom of an illness but not an illness itself. Fever is the body’s way of reacting to help fight the illness. Your child’s discomfort and the illness causing the fever is often more of a concern than the high temperature reading. Body temperature is accurately measured with a thermometer. Digital thermometers are safer than glass thermometers because these do not contain mercury.

Normal body temperature range is 98.6 degrees F to 100 degrees F. Your child's temperature can change with activity, eating, the amount of clothing he wears, or the time of day. There are three ways to take a temperature:

  • by rectum
  • by mouth
  • by underarm


By rectum:

If your child is 1 month old up to 5 years old, check his rectal temperature if you think he has a fever. (Some 4 year olds may be able to use oral thermometers.)

Rectal temperatures should not be taken if:

  • your child is less than one month old
  • your child was born prematurely (wait until your child’s due date plus one month to do rectal temperatures)
  • your child has diarrhea
  • your child is on chemotherapy
  • your child has an illness that affects the immune system
  • your child has had surgery in the anal area (ask the physician when to start rectal temperatures)
  • your child’s physician has instructed you not to use rectal temperatures
  • If available, use a probe cover with your thermometer. If you do not have probe covers use separate thermometers to take rectal and oral temperatures.
  • Use a water-based lubricant (such as K-Y Jelly®) on the end of the thermometer.
  • Place the infant on his back with his legs up or on his stomach in your lap with his legs down.
  • Put the thermometer ½ inch into the rectum if your infant is 1 month – 1 year old, or 1 inch into the rectum if your child is over 1 year old. Keep your child's legs together so he doesn't push the thermometer out. Hold it in place until it beeps. Remove it, wipe off the end with a tissue and read it.
  • Be sure to wash your hands thoroughly with warm, soapy water.

By mouth:

Older children can usually have their temperature taken by mouth. Children 4-5 years old usually object to rectal temperatures. A child may not be able to hold a thermometer in his mouth for very long until they are 5-6 years old. A digital thermometer only takes about a minute to get a reading.

  • If available, use a probe cover with your thermometer.
  • Place the thermometer under the side of your child's tongue until the thermometer beeps. Tell your child to keep lips firmly closed but not to bite the thermometer. It is often helpful to have the child hum to help pass the time and keep the mouth shut. The digital thermometer will beep when it is ready to be read. Remove the thermometer and read it.
  • Remember that cold or hot drinks or chewing gum can change oral temperature. Wait 15 minutes after eating or drinking before taking a temperature by mouth.

By underarm:

Studies show that underarm temperatures are only accurate for infants less than one month old.

Using this method for other children will not always provide a reliable temperature measurement. Use this method only if your child has a condition that does not allow rectal temperatures or if he cannot use an oral thermometer.

  • If available, use a probe cover with your thermometer.
  • Put the end of the thermometer in the center of your child's armpit. Be sure the thermometer is only between skin and that clothes are not in the way.
  • Bring your child's arm down, close to the side.
  • Hold the thermometer tightly in place until it beeps (may take up to 5 minutes). If your child squirms and you cannot keep the arm tightly closed against the body with the thermometer in place you will not get an accurate reading.
  • Remove the thermometer and read it.

How to care for your thermometer

  • After using the thermometer, remove the probe cover. Clean the thermometer end with a soapy cotton ball or tissue and cool water. Rinse it with cool water.
  • Store it in a safe place out of reach of children.

When to call your child’s doctor

  • Call your child’s doctor if your child's temperature is more than 101.5 degrees F or 38.5 degrees C, or follow the temperature guidelines from your doctor.
  • If you used the underarm method, call the doctor even if the thermometer does not show a high temperature if your child appears to be ill.
  • When you report your child’s temperature, tell the doctor which method you used: by rectum, by mouth or by underarm.

Disclaimer: This information is not intended to substitute or replace the professional medical advice you receive from your child's physician. The content provided on this page is for informational purposes only, and was not designed to diagnose or treat a health problem or disease. Please consult your child's physician with any questions or concerns you may have regarding a medical condition.

Reviewed: 06/2018

(757) 668-7000