How to Take Baby’s Temperature (Without Losing Your Cool)

A mother, or any other caregiver for children, has to be able to take her baby’s temperature occasionally. The first time might make you nervous, but you will soon be an old pro at it.

First, be thankful that you’ll probably never need to use an old-fashioned fever thermometer like your grandmother and maybe even your mother used. These were made of glass, they were usually filled with mercury and they were next to impossible to read unless you were holding it just right in front of your eyes  and had exceptional vision. They also had to be held in place for three minutes to get an accurate reading; three minutes of waiting and holding the thermometer in place while your baby or toddler squirms or cries.

But now, you can choose between several types of thermometers that are available that are easy to use and easy to read. These include:

  • Digital thermometers that can be used to take an temperature orally with the thermometer in the mouth, rectally with the thermometer in the rectum, or axillary with the thermometer placed in the armpit. These use heat sensors to measure body temperature. This kind of thermometer gives the most accurate reading, but oral and rectal readings are more accurate than axillary readings. There are rectal and oral digital thermometers. Rectal thermometers have a short tip. Most digital thermometers beep once or a few times when the temperature is ready to be read and you can see the digital readout easily.
  • Ear thermometers that read the temperature in your child’s ear canal. These use an infrared scanner to measure the body temperature deep in the ear canal. However, they may not be as accurate in children under age 6 months as with older children.
  • Temporal artery thermometers that use an infrared scanner to measure the temperature of the forehead. These can be used even if your child is asleep but may not be as accurate as an oral or rectal thermometer.
  • Avoid using temperature strips, which are placed on the forehead for a reading. These are not as accurate as thermometers.

Temperature readings can vary greatly depending on whether they are taken orally, rectally, in the armpit, or the forehead. The most accurate way to take baby’s temperature is to measure rectally. An armpit temperature may not be as accurate as a rectal or oral reading.

Do not take an oral temperature until about the child is about age 4, when the child is able to follow directions and keep the tip of the thermometer under the tongue with a closed mouth

If your baby is under three months old, take a temperature rectally using a digital thermometer. You will need to lubricate the tip of the thermometer with petroleum jelly (Vaseline) or a water-soluble lubricant. The instructions that came with the thermometer will say which kind of lubricant should be used. You may have to turn the thermometer on or clear the last reading before your take your baby’s temperature.

Place the baby face up on a flat surface such as a changing table and take the baby’s diaper off. Spread the baby’s buttocks and gently insert the lubricated tip of the thermometer about half an inch into the baby’s anus. Stop if you feel there is any resistance. Do not force it. Hold the thermometer in place gently between two fingers and cup the rest of your hand around the baby’s buttocks. When you hear the thermometer beep—it usually takes about 30 seconds—remove it and read the temperature.

In a child older than 6 months, you can take a temperature under the arm. To take an axillary reading, remove the child’s shirt or top so that the thermometer will be touching only skin. Place the thermometer under the child’s arm. Hold the arm firmly against the child’s side with the thermometer in place and wait to hear the beep.

For older children, you can take their temperature orally. Place the tip of the thermometer under the tongue and tell the child to keep their mouth closed until you hear the beep. If your child’s nose is stuffed up and the child must breathe through the mouth, take the temperature rectally.

No matter which way you take a temperature using a digital thermometer, clean it before and after each use. Wipe it down after use with rubbing alcohol or soapy water and then rinse it with water. Let it air dry and then put it away.

You should ask your child’s pediatrician for guidelines on what to do if your child has an elevated temperature. The doctor may have a printout that you can keep handy that will have instructions on what to do or what to look for. If you child has an elevated temperature, tell the doctor or the office staff what the reading is, when you took it, and what method you used.

Generally, your child has a fever if a rectal or forehead temperature is over 100.4 F (38 C) or higher, an oral temperature of 100 F (37.8 C) or higher, or an armpit temperature of 99 F (37.2 C) or higher. If you’re in doubt about an armpit temperature reading, use another method to confirm the results.

Your child’s pediatrician will give you guidelines on when to contact him or her about a fever. But, in general, call the doctor if your baby is under age 3 months and has a rectal temperature at or above 100.4 F (38 C). If your child is age 3 to 6 months and has a temperature higher than 102 F (38.9 C), call the doctor. Call if the temperature reading is above 100.4 F and your child is irritable or lethargic, or has other symptoms like diarrhea or a cough.

Valerie DeBenedette
Valerie DeBenedette is an experienced health and medical writer who lives about an hour north of New York City with a dog that is smaller than her cat. Her work has appeared in magazines, newspapers, newsletters, and on websites. She is a member of the National Association of Science Writers.

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