If your baby has a fever, learn how to use a thermometer to measure the axillary and oral temperatures.

June 11, 2015

Fever occurs when the body's temperature rises to 99.4° or higher. A thermometer is used to measure body temperature; it can be placed under the tongue to measure the oral temperature or in the center of the armpit to measure the axillary temperature. These two methods are used to measure temperature in children older than 3 months old. Consult a doctor for the best way to measure temperature in an infant younger than 3 months.

Check the baby products aisle of the drugstore or grocery store for thermometers made specifically for babies and toddlers. Always read the manufacturer's instructions before using the thermometer to measure fever correctly.

  • Digital thermometers are the most common type that measures temperature with either the oral or axillary method. They have a probe at one end and a display window at the other end. A series of beeps indicates the temperature reading is ready.
  • Pacifier thermometers measure only oral temperature; this may not be as accurate. For fevers over 102°, retake the temperature with a different type of thermometer.
  • Never use a glass mercury thermometer with your baby. The glass can break, leaking mercury in the mouth or on the skin, causing serious injury. Call your doctor or the local health department to find out how to dispose of a glass mercury thermometer.

If you don't get a temperature reading in the display window, check the battery of your digital thermometer or read the instructions again to make sure you've followed directions correctly.

How to Measure the Oral Temperature

An oral temperature higher than 100.4° is considered a fever. Follow these quick, easy methods for taking your baby's oral temperature.

  1. If your baby has had food or drink, wait 20 to 30 minutes before you measure his temperature.
  2. Turn on the thermometer and make sure the screen does not display a reading from a previous use. Read the thermometer's instructions to learn how to clear an old reading.
  3. Hold the baby on your lap.
  4. Place the probe tip of the thermometer under your baby's tongue and wait until he closes his lips around it.
  5. Wait to hear a series of beeps that indicate a completed reading.
  6. Remove the thermometer.
  7. Write down the time of day and the temperature reading.

How to Measure the Axillary Temperature

An axillary temperature higher than 99.4° is considered a fever, and it is usually 1° lower than an oral temperature. This axillary method is not as accurate as the oral method, but you may prefer to use it if your baby cannot hold a thermometer in his mouth. Follow these guidelines for taking your baby's axillary temperature.

  1. If your infant has just had a bath, wait 15 minutes before measuring temperature.
  2. Place the baby on your lap.
  3. Remove your baby's shirt and place the probe of the thermometer in the center of the armpit. The probe must not touch any clothing, only skin.
  4. Gently hold your baby's arm down and across the chest to hold the probe in place.
  5. Wait to hear a series of beeps that indicate the reading is complete.
  6. Remove the thermometer.
  7. Write down the time of day and the temperature reading.

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