Taking Baby'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 4 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 is 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.

  • Underarm (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 is 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. 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. 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.

You should avoid other 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 he or she looks—and your gut feeling should help make the decision on whether to call your 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 your 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 awaken easily (is lethargic), looks ill, or isn't responsive

  • If a child has other concerning symptoms such as decreased urination, stiff neck, severe headache, trouble breathing, earache, throat pain, or seizure

When you call your child's healthcare provider, give him or her 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 your healthcare provider about any symptoms that your child may have. Try to stay relaxed. Listen to his or her 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 your healthcare provider before giving medicine. Follow the package instructions carefully or the dosing instructions given to you by your healthcare 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 he or she is not 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 him or her shiver and can make the temperature go higher. Never use alcohol baths or wipes because the alcohol can be absorbed through the skin and cause serious illness.

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

Fever and children

Always use a digital thermometer to check your child’s temperature. Never use a mercury thermometer.

For infants and toddlers, be sure to use a rectal thermometer correctly. A rectal thermometer may accidentally poke a hole in (perforate) the rectum. It may also pass on germs from the stool. Always follow the product maker’s directions for proper use. If you don’t feel comfortable taking a rectal temperature, use another method.

Here are guidelines for fever temperature. Ear temperatures aren’t accurate before 6 months of age. Don’t take an oral temperature until your child is at least 4 years old.

Infant under 3 months old:

  • Ask your child’s healthcare provider how you should take the temperature.

  • Rectal or forehead temperature of 100.4°F (38°C) or higher, or as directed by the provider

  • Armpit temperature of 99°F (37.2°C) or higher, or as directed by the provider

Child age 3 to 36 months:

  • Rectal, forehead (temporal artery), or ear temperature of 102°F (38.9°C) or higher, or as directed by the provider

  • Armpit temperature of 101°F (38.3°C) or higher, or as directed by the provider

Child of any age:

  • Repeated temperature of 104°F (40°C) or higher, or as directed by the provider

  • Fever that lasts more than 24 hours in a child under 2 years old. Or a fever that lasts for 3 days in a child 2 years or older.