Thermometer basics: Taking your child’s temperature

By Mayo Clinic Staff

If your child feels warm or doesn’t feel well, it’s probably time to take your child’s temperature. Sounds simple enough, but if you’re new to it, you might have questions. Which type of thermometer is best? Are thermometer guidelines different for babies and older children? Here’s what you need to know to take your child’s temperature.

A glass mercury thermometer was once a staple in most medicine cabinets. Today, mercury thermometers aren’t recommended because they can break and release mercury vapor, which can be inhaled. When choosing a thermometer, consider these options:

• Digital thermometers. These thermometers use electronic heat sensors to record body temperature. Digital thermometers can be used to record temperature in different parts of the body: rectum, mouth or armpit. A rectal thermometer records the temperature in the rectum. An oral thermometer records it in the mouth. And an axillary thermometer records the temperature in the armpit. Armpit temperatures are typically the least accurate of the three.
• Digital ear thermometers. These thermometers are called tympanic membrane thermometers. They use an infrared scanner to measure the temperature inside the ear canal. Remember that earwax or a small, curved ear canal can affect accuracy.
• Temporal artery thermometers. These thermometers use an infrared scanner to measure the temperature of the temporal artery in the forehead. You can use this type of thermometer even while a child is asleep.

Digital pacifier thermometers and fever strips are not recommended.

Carefully read the instructions that come with the thermometer. Clean the tip before and after each use, following the instructions for your particular thermometer. If you plan to use a digital thermometer to take a rectal temperature, get another digital thermometer for oral use. Label each thermometer, and don’t use the same thermometer in both places.

For safety and to ensure the thermometer stays in place, never leave your child unattended while you’re taking the temperature.

The best type of thermometer or the best place to insert it, in some cases, depends on your child’s age.

• Birth to 3 months. Use a regular digital thermometer to take a rectal temperature. New research suggests that a temporal artery thermometer also might provide accurate readings in newborns.
• 3 months to 4 years. In this age range, you can use a digital thermometer to take a rectal or an armpit temperature. Or you can use a temporal artery thermometer. Wait until your baby is at least 6 months old to use a digital ear thermometer. If you use another type of thermometer to take a young child’s temperature and you question the results, take a rectal temperature.
• 4 years and older. By age 4, most kids can hold a digital thermometer under the tongue for the short time it takes to get an oral temperature reading. You also can use a digital thermometer to take an armpit temperature, a temporal artery thermometer or a digital ear thermometer.

• Rectal temperature. Turn on the digital thermometer and lubricate the tip of the thermometer with a lubricant, such as petroleum jelly. Lay your baby or child on the back, lift the thighs, and insert the lubricated thermometer 1/2 to 1 inch (1.3 to 2.5 centimeters) into the rectum. Or you can place your child on the belly on your lap or another firm surface. If you put your child belly down, put your hand against the lower back to hold your child in place.

  Never try to force a rectal thermometer past any resistance. Hold the thermometer in place until the thermometer signals that it’s done. Remove the thermometer and read the number.

• Oral temperature. Turn on the digital thermometer. Place the tip of the thermometer under your child’s tongue toward the back of the mouth and ask your child to keep lips closed. Remove the thermometer when it signals that it’s done and read the number. If your child has been eating or drinking, wait 30 minutes to take your child’s temperature by mouth.
• Armpit temperature. Turn on the digital thermometer. When you place the thermometer under your child’s armpit, make sure it touches skin, not clothing. While the device reads your child’s temperature, hug your child, keeping the side holding the thermometer against your chest. Keep the thermometer tightly in place until the thermometer signals that it’s done. Remove the thermometer and read the number.
• Ear temperature. Turn on the thermometer. Gently place the thermometer in your child’s ear. Follow the directions that come with the thermometer to ensure you insert the thermometer the proper distance into the ear canal. Hold the thermometer tightly in place until the thermometer signals that it’s done. Remove the thermometer and read the number.
• Temporal artery temperature. Turn on the thermometer. Gently sweep the thermometer across your child’s forehead. Remove the thermometer and read the number.

When reporting a temperature to your child’s care team, give the reading and explain how the temperature was taken.

A fever is a common sign of illness, but that’s not necessarily a bad thing. In fact, fevers seem to play a key role in fighting infections. If your child is older than 6 months and is drinking plenty of fluids, sleeping well and continuing to play, there’s usually no need to treat the fever.

If you want to give your child medicine to treat a fever, stick to acetaminophen (Tylenol, others) until age 6 months. However, for children younger than age 3 months, don’t give acetaminophen until your baby has been seen by your healthcare team. Never give more acetaminophen than recommended on the label for your child. Be aware that some combination over-the-counter medicines might contain acetaminophen as an ingredient.

If your child is age 6 months or older, ibuprofen (Advil, Children’s Motrin, others) is OK too. Read the label carefully for proper dosage. Don’t use aspirin to treat a fever in anyone age 18 years or younger.

Your child has a fever if your child has:

• A rectal, ear or temporal artery temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher.
• An oral temperature of 100 degrees Fahrenheit (37.8 degrees Celsius) or higher.
• An armpit temperature of 99 degrees Fahrenheit (37.2 degrees Celsius) or higher.

Keep in mind that an armpit temperature might not be accurate. If you’re in doubt about an armpit temperature reading, use another method to confirm the results.

In general, contact your child’s care team if:

• Your child is younger than age 3 months and has a rectal temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher.
• Your child is age 3 to 6 months and has a temperature up to 101 degrees Fahrenheit (38.3 degrees Celsius) and seems unusually irritable, lethargic or uncomfortable, or has a temperature higher than this number.
• Your child is age 6 to 24 months and has a temperature higher than 101 degrees Fahrenheit (38.3 degrees Celsius) that lasts longer than one day but shows no other signs. If your child has other signs, such as a cold, cough or diarrhea, you might call your child’s care team sooner based on the severity of the other signs.
• Your child with a fever has a febrile seizure for the first time.