Frequently asked questions about fever in children

What is a fever?


The definition of fever depends upon the site where it is measured:


  • Rectal temperature above 100.4°F (38°C)
  • Oral temperature above 99.5°F (37.5°C)
  • Axillary (armpit) temperature above 99°F (37.2°C)
  • Digitial pacifier temperature above 100°F (37.8°C)
  • Ear temperature above 100.4°F (in rectal mode) or 99.5°F (in oral mode)


How do I measure my child's temperature?


The best method to measure temperature depends upon several factors. In all cases, rectal temperatures are the most accurate. However, measurements of temperature in the mouth (for children older than 4 or 5 years) or ear (for children older than 6 months) are accurate when done properly. Temperatures measured in the armpit are least accurate, but may be useful with an infant younger than 3 months as a first test. If the armpit temperature is over 99°F (37.2°C), a rectal temperature should be measured.


Glass thermometers are not recommended due to the potential risks of exposure to mercury, which is toxic. If another (digital) thermometer is not available, be sure to carefully "shake down" the glass thermometer before use.


Measuring rectal temperature


  • The child or infant should lie down on their stomach across an adult's lap.
  • Apply a small amount of petroleum jelly (e.g., Vaseline) to the end of the thermometer.
  • Gently insert the thermometer into the child's anus. The silver tip of the thermometer should be 1/4 to 1/2 inch inside the rectum.
  • Hold the thermometer in place. A glass thermometer requires 2 minutes while most digital thermometers need less than 1 minute.


Measuring oral temperature


  • Clean the thermometer with cool water and soap. Rinse with water.
  • Do not measure the temperature in a child's mouth if he or she has consumed a hot or cold food or drink in the last 30 minutes.
  • Place the tip of the thermometer under the child's tongue towards the back. Ask the child to hold the thermometer with his or her lips.
  • Keep the lips sealed around the thermometer. A glass thermometer requires about 3 minutes while most digital thermometers need less than 1 minute.


Measuring an armpit temperature


  • Place the tip of the thermometer in the child's dry armpit.
  • Hold the thermometer in place by holding the child's elbow against the chest for 4 to 5 minutes.


Measuring an ear temperature


  • Ear thermometers are not reliable in infants less than 6 months old.
  • To measure temperature accurately in the ear, the parent must pull the child's outer ear backwards before inserting the thermometer.
  • The ear probe is held in the child's ear for about 2 seconds.
  • If the child has been outside on a cold day, wait 15 minutes before measuring the ear temperature.
  • Ear tubes and ear infections do NOT affect the accuracy of an ear temperature.



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