Taking a Baby's or Child's Temperature

Thermometers have changed a lot in the last 20 years. Mercury thermometers are no longer used because mercury is a toxic metal. Digital thermometers have replaced them. Contact your local health department, waste disposal authority, or fire department to ask how to safely get rid of mercury thermometers.

If you need to take an infant's or child's temperature, you have 5 digital choices:

  • Rectal (in the bottom) temperature.  Several digital rectal thermometers are available for taking rectal temperatures. Parents worry about these because they think they may insert them incorrectly. But there's little risk for injury if you use a thermometer made for taking a rectal temperature. Most thermometers have an alarm to tell you when the measurement is done. They also have a digital readout. If you choose to take rectal temperatures, use a digital rectal thermometer with the short probe. This reduces the chance that your baby may be injured. Make sure you label the thermometer so that you know it's for rectal use only. A rectal thermometer is the most accurate, especially for babies younger than 3 months old.

  • Armpit (axillary) temperature. Any of the digital thermometers can be used in the armpit. A disk-shaped thermometer fits most comfortably. The whole disk is covered when the arm is brought against the chest wall. Make sure there's nothing (such as clothing) between the child's skin and the thermometer. The temperature appears on a digital readout when the alert sounds. Axillary thermometers may be used for babies ages 3 months and older.

  • Ear (tympanic) temperature. The ear thermometer is the quickest of the digital thermometers. It works in only a second. To get an accurate temperature, the thermometer must be pointed toward the eardrum. Earwax may make it hard to get an accurate reading. Ear thermometers also may not be accurate for newborns and older infants. For this reason they're advised for babies older than 6 months. They must be placed carefully to get an accurate reading. You may have some trouble using this type of thermometer at first. With practice, you’ll find it’s easy to do.

  • Forehead (temporal artery) temperature. This thermometer is very easy to use and can be used on all ages. It's as accurate as a rectal thermometer but with less discomfort. It’s also less disturbing to a newborn. It measures the core body temperature through the artery on the forehead. Sunlight and cold temperatures outside may affect readings.

  • Mouth (oral) temperature. Any digital thermometer can be used by mouth. But this method is advised for children age 4 and older, as it can be hard for younger children to do. To get a reading, place the tip of the thermometer under the child's tongue. Then have the child close their lips gently around the thermometer. They shouldn't bite down on it with their teeth. They must keep the thermometer in place until they hear a beep and the temperature appears on the digital readout.

Don't use other types of fever "detectors." These are strips that you place on a child's forehead or pacifiers that have a dot that changes color to show a fever. These aren't as reliable as a standard thermometer. 

When using any of the digital devices, read and carefully follow the directions.

When to call the healthcare provider

One of the most important things to remember about fever in children is that a child's appearance—how sick they look—and your gut feeling should help make the decision on whether to call the healthcare provider. Think of a fever as a symptom of illness, but not an illness itself. Children can be extremely or even critically ill and not have a fever. They can also have a high fever and be only mildly ill, or even running around as if nothing was wrong. Your decision to call should be based on all this information, with a few exceptions that should always be followed.

Always call the healthcare provider about a fever in your child in these cases:

  • For specific fever temperature guidelines, see "Fever and children" below

  • Any fever in a child who doesn't wake up easily (is lethargic), looks ill, or isn't responsive

  • If a child has other concerning symptoms like decreased urination, stiff neck, severe headache, trouble breathing, earache, throat pain, persistent vomiting, abnormal skin rashes or seizures

When you call your child's healthcare provider, give them the actual reading on the thermometer and say where the temperature was taken. Was it in the ear, the underarm, the forehead, or the rectum? Be ready to tell the provider about any symptoms that your child may have. Try to stay relaxed. Listen to the provider's questions and answer them as accurately as possible.

How to treat it

Fever is part of the body’s natural immune response. It helps fight infection. But a fever can make an infant or child fussy and uncomfortable. You may wish to treat the fever with acetaminophen or ibuprofen. If your child is under the age of 2 years, talk with their healthcare provider before giving medicine. Follow the package instructions carefully or the dosing instructions given to you by the provider. When given correctly, these medicines usually will make the fever go down, although it may not return to normal. If a temperature doesn't respond to fever medicine, this doesn't mean that a child is more seriously ill. If the fever does come down, expect it to rise again in about 3 to 4 hours, as the medicine wears off. You may give another dose, if needed, every 6 hours, or as directed by your child's healthcare provider.

Before giving your child medicine, make sure they aren't dressed too warmly. Loose, comfortable clothing is best. A lukewarm bath may also help your child feel better. Avoid making your child cold, such as with a cold bath or ice packs. This will make them shiver and can make the temperature go higher. Never use alcohol baths or wipes because the alcohol can be absorbed through the skin. This can cause serious illness.

While fever itself isn't dangerous, it can cause dehydration. Make sure your child is drinking plenty of fluids. If you have any concerns about your child's fever and symptoms, speak with their healthcare provider. 

Fever and children

Use a digital thermometer to check your child’s temperature. Don’t use a mercury thermometer. There are different kinds and uses of digital thermometers. They include:

  • Rectal. For children younger than 3 years, a rectal temperature is the most accurate.

  • Forehead (temporal). This works for children age 3 months and older. If a child under 3 months old has signs of illness, this can be used for a first pass. The provider may want to confirm with a rectal temperature.

  • Ear (tympanic). Ear temperatures are accurate after 6 months of age, but not before.

  • Armpit (axillary). This is the least reliable but may be used for a first pass to check a child of any age with signs of illness. The provider may want to confirm with a rectal temperature.

  • Mouth (oral). Don’t use a thermometer in your child’s mouth until he or she is at least 4 years old.

Use the rectal thermometer with care. Follow the product maker’s directions for correct use. Insert it gently. Label it and make sure it’s not used in the mouth. It may pass on germs from the stool. If you don’t feel OK using a rectal thermometer, ask the healthcare provider what type to use instead. When you talk with any healthcare provider about your child’s fever, tell him or her which type you used.

Below are guidelines to know if your young child has a fever. Your child’s healthcare provider may give you different numbers for your child. Follow your provider’s specific instructions.

Fever readings for a baby under 3 months old:

  • First, ask your child’s healthcare provider how you should take the temperature.

  • Rectal or forehead: 100.4°F (38°C) or higher

  • Armpit: 99°F (37.2°C) or higher

Fever readings for a child age 3 months to 36 months (3 years):

  • Rectal, forehead, or ear: 102°F (38.9°C) or higher

  • Armpit: 101°F (38.3°C) or higher

Call the healthcare provider in these cases:

  • Repeated temperature of 104°F (40°C) or higher in a child of any age

  • Fever of 100.4°F (38°C) or higher in baby younger than 3 months

  • Fever that lasts more than 24 hours in a child under age 2

  • Fever that lasts for 3 days in a child age 2 or older

Online Medical Reviewer: Donna Freeborn PhD CNM FNP
Online Medical Reviewer: Heather M Trevino BSN RNC
Online Medical Reviewer: Liora C Adler MD
Date Last Reviewed: 4/1/2022
© 2000-2024 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.