Definition of Fever

  • Rectal temperature above 100.4°F (38.0°C).
  • Oral temperature above 99.5°F (37.5°C).
  • Axillary (armpit) temperature above 99.0°F (37.2°C).
  • Pacifier temperature above 100°F (37.8°C).  New digital electronic ones are accurate.
  • Ear (tympanic) temperature above 100.4°F (if in rectal mode) or above 99.5°F (if in oral mode).  (Note: Not reliable for less than 6 months old.)
  • Temporal artery (TA) temperature above 100.4 F (38.0 C) (Note: more reliable than tympanic thermometers, but not to be used for children under 6 months old)

Where to Take the Temperature

  • Temperatures measured rectally are the most accurate.  Temperatures measured orally, by electronic pacifier, or by ear canal are also accurate if done properly.  Temperatures measured in the armpit are the least accurate, but they are better than no measurement.
  • Age less than 3 months old (90 days old):
    An armpit temperature is preferred for reasons of safety and is adequate for screening.  If the armpit temperature is above 99°F (37.2°C), check it with a rectal temperature.  The reason you need to take a rectal temperature for young infants is that if they have a true fever, they need to be evaluated immediately.
  • Age less than 4 or 5 years old:
    A rectal or electronic pacifier temperature is preferred.  An axillary (armpit) temperature is adequate for screening if it is taken correctly.  An ear thermometer can be used after 6 months old.
  • Age older than 4 or 5 years old:
    Take the temperature orally (by mouth) or by ear thermometer.

How to Take Rectal Temperatures

  • Have your child lie stomach down on your lap.
  • Put some petroleum jelly on the end of the thermometer and on the opening of the anus.
  • Slide the thermometer gently into the opening of the anus for about 1-inch.  If your child is less than 6 months old, put it in only about ¼ to ½ inch (inserting until the silver tip disappears is about ½ inch).
  • Hold your child still and leave the thermometer in 2 minutes with a glass thermometer (about 20 seconds with a digital electronic thermometer).
  • Your child has a fever if the rectal temperature is above 100.4°F (38°C).

How to Take Armpit Temperatures

  • Put the tip of the thermometer in an armpit.  Make sure the armpit is dry.
  • Close the armpit by holding the elbow against the chest for 4 or 5 minutes.
  • Your child has a fever if the armpit temperature is above 99.0°F (37.2°C).  If you have any doubt, take your child's temperature by rectum.  

How to Take Oral Temperatures

  • Be sure your child has not had a cold or hot drink in the last 30 minutes.  
  • Put the tip of the thermometer under one side of the tongue and toward the back.  It's important to put it in the right place.  
  • Have your child hold the thermometer in place with his lips and fingers (not teeth) for 3 minutes with a glass thermometer (about 30 seconds with a digital electronic thermometer).  Keep the lips sealed.
  • Your child has a fever if the temperature is above 99.5°F (37.5°C)

How to Take a Digital Electronic Pacifier Temperature

  • Have your child suck on the pacifier until it reaches a steady state, and you hear a beep.
  • This usually takes 3 to 4 minutes.
  • Your child has a fever if the pacifier temperature is above 100°F (37.8°C)

How to Take an Ear Temperature

  • This thermometer reads the infrared heat waves released by the eardrum.
  • An accurate temperature depends on pulling the ear backward to straighten the ear canal (back and up if over 1 year old).
  • Then aim the tip of the ear probe midway between the opposite eye and earlobe.
  • The biggest advantage of this thermometer is that it measures temperatures in less than 2 seconds.  It also does not require cooperation by the child and does not cause any discomfort.
  • Limitation: if your child has been outdoors on a cold day, he needs to be inside for 15 minutes before taking the temperature.  Earwax, ear infections and ear tubes, however, do not interfere with accurate readings.

Disclaimer: This information is not intended be a substitute for professional medical advice. It is provided for educational purposes only. You assume full responsibility for how you choose to use this information.

Pediatric HouseCalls Online. Copyright © 2000-2004 Barton Schmitt, M.D. FAAP

Reviewed 8/2004

Revised 8/2003

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