A rectal thermometer is the most accurate way to take a temperature.

To take a rectal temperature:

• Apply a lubricant jelly or petroleum jelly, such as Vaseline, on the bulb of the thermometer, so that you can insert it easily.
• Choose a quiet place so that the child won’t be distracted or move around too much. When measuring the temperature of babies or small children:
  • Place your child faceup with legs bent toward the chest with your hand on the back of the thighs or holding the feet as if you were changing a diaper.
  • Place the child facedown on your lap or on a flat covered or padded surface, such as a bed.
• Gently insert the bulb end of the rectal thermometer about 0.6 in. (1.5 cm) to 1 in. (2.5 cm) into the anal canal. Don’t force it into the rectum. Hold the thermometer in place with two fingers close to the anal opening (not near the end of the thermometer).
• Leave the thermometer in place for the required amount of time, usually a minute. Some digital thermometers give a series of short beeps when the reading is done. Time yourself with a watch or clock.
• Remove the thermometer and read it.
• Clean a digital thermometer with cool, soapy water, and rinse it off before putting it away.
• After a thermometer has been used to take a rectal temperature, do not use it to take an oral temperature.