How do I take baby's temperature?

Q: How do I take my baby's temperature? She is 9 months old. Should I use a rectal thermometer? And, if so, how long should I wait before reading it?
A: Sara, there are many different options for taking your baby's temperature. The option you choose depends on your doctor's recommendation and your comfort level.

The standard ways to take an infant's temperature are with the ear thermometer, or with a plastic digital thermometer under the arm or rectally. (Don't use a glass mercury thermometer since it can break and leak toxic mercury vapor.) These thermometers tell you when it's time to read the temperature. The ear thermometer displays the temperature immediately while the digital thermometer beeps when it reaches your child's temperature reading.

Although the rectal temperature is considered most accurate, it can be uncomfortable for the child and parent, and it exposes you more to your child's germs. In most cases, the ear thermometer and underarm (axillary) digital thermometer are accurate enough.

Here are the basic techniques for taking your baby's temperature:

Ear thermometer:
  • Cover the thermometer with a fresh plastic tip.
  • With one hand, hold your child's ear steady.
  • With the other hand, gently insert the thermometer into your child's ear canal until you get a tight seal.
  • Press the start button and read the temperature displayed.
  • Discard the used plastic tip.
  • Underarm digital thermometer:
  • Place the tip of the thermometer under your child's armpit, between the bare skin of the arm and chest.
  • Hold her arm tightly against her chest.
  • When you hear the beep, remove and read the thermometer.
  • Rectal digital thermometer:
  • Clean the tip of the thermometer with soap and cool water.
  • Put a small amount of lubricant (such as petroleum jelly) on the tip, and turn on the thermometer.
  • Lay your child belly-down across your lap with his bottom exposed.
  • Gently insert the thermometer ½ to 1 inch into his anus. Hold the thermometer in place by cupping your hand over your baby's bottom.
  • When you hear the beep, remove and read the thermometer.
  • Turn off the thermometer. Wash the thermometer and your hands with soap and warm water.
  • Newer types of thermometers include a pacifier thermometer, which a baby sucks on, and a temporal artery thermometer, which is rolled across a child's forehead. These thermometers are currently being evaluated for accuracy. You can ask your doctor for advice about them.

Karen Sokal-Gutierrez M.D., M.P.H. Pediatrician