How to Take an Infant's Body Temperature the Right Way

Over the years, you may have noticed just how much modern thermometers have changed. Gone are mercury thermometers, which can turn from a useful household tool to a toxic hazard if they break. Now, you can easily acquire a sturdier, safer digital thermometer for taking temperatures.

Even so, not all thermometers are built the same, and how you take your child’s temperature must differ depending on their age. Here’s how to properly take an infant’s temperature with a digital thermometer.

If your child is three months old or younger, taking their temperature rectally is the most accurate method at this stage of life. Pencil thermometers are suitable for rectal, oral, and underarm readings, making them a good option if you want to use different methods.

First, be sure to put a diaper or cloth across your lap, as taking a rectal temperature can potentially induce a bowel movement in your baby. Next, place your child over your lap, on their back or stomach. Then, put a small amount of petroleum jelly on the tip of the thermometer. Insert the thermometer gently into the rectum, only up to just ½ inch (approximately just over 1 centimeter). Hold the thermometer in place until it successfully registers your child’s temperature.

Once your baby has grown a little older, you can start using a temporal thermometer instead. This type of thermometer measures the temperature of the temporal artery in the forehead. This makes the process of getting their temperature taken more comfortable for the baby, and you can even do it while they’re asleep. Some temporal thermometers require direct contact with your baby’s forehead, while others do not, so read the instructions carefully first before using.

However, as convenient as a temporal thermometer is, a rectal temperature is still the most accurate way to take your child’s temperature. The process for using a rectal thermometer for an older baby is similar to how you take a newborn’s temperature, but you’ll need to insert the thermometer about an inch (about 2.5 centimeters) into the rectum instead.

If your baby is six months old and up, their ear canals are likely big enough that you can instead use an ear thermometer for taking their temperature. These thermometers measure the heat waves coming from the patient’s eardrum. Simply place the thermometer in your child’s ear to take their temperature. Read the instructions carefully to know how far you have to insert it into the ear canal, as it can vary depending on the model and manufacturer.

At this age, you can also use the rectal, temporal artery, or axillary (armpit) method to take your child’s temperature. A rectal temperature remains the most accurate, but the other methods are still reliable, so it’s up to your personal preference.

Many outside factors can affect your baby’s temperature and result in an inaccurate reading. Don’t take their temperature immediately after a bath, swaddling, crying, or exercising, as these can all temporarily raise your baby’s temperature. It’s also important to use the correct thermometer depending on the baby’s age, as temporal or ear thermometers may not give an accurate reading for younger infants.

Most of the time, a fever is nothing to worry about. However, if their temperature reaches a certain threshold or your child is experiencing other symptoms, it may be time to call their doctor for a proper diagnosis and medical care.

Call your pediatrician if:

Using the right thermometer makes it easier to get accurate readings while also keeping your child safe and comfortable. As your baby grows and becomes more communicative, you can decide together which thermometer they prefer when they need their temperature taken. By the time they are four years old or older, an oral temperature is best for accuracy, but the other methods can still be used if your child prefers them.

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