Taking Baby's Temperature

Thermometers have changed a lot in the last few decades. 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 for information on how to properly get rid of mercury thermometers.

As a parent who needs to take an infant's or child's temperature, you now have 4 digital options:

  • Rectal 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 designed for taking a rectal temperature. Most thermometers have an audible alert to tell you when the measurement is done. They also have a digital readout.

  • Axillary (underarm) temperature. Any of the digital thermometers can be used in the armpit, but a disk-shaped thermometer fits most comfortably. The entire disk is covered when the arm is brought against the chest wall. The temperature appears on a digital readout when the alert sounds. Axillary thermometers may be used for babies ages 3 months and older.

  • Tympanic (ear) temperature. The tympanic thermometer is the quickest of the digital thermometers. It works in only a second. In order to get an accurate temperature, the thermometer must be pointed toward the eardrum. Earwax (cerumen) may make a tympanic thermometer less accurate. Tympanic 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 difficulty using this type of thermometer in the beginning. With practice, you’ll find it’s an easy process.

  • Temporal artery thermometry. This thermometer is extremely easy to use. It is 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. If you choose to take rectal temperatures, choose a digital rectal thermometer with the short probe. This reduces the risk for injury.

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 health care 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 also can have a high fever and be only mildly ill, or even running around as if nothing were wrong. Your decision to call should be based on all this information with a few ironclad exceptions.

When to call the doctor

These are instances when you should call your health care provider about a fever in your child:

  • If a child younger than age 3 months has a rectal or tympanic temperature above 100.4° F (38° C)

  • If an older infant or child repeatedly has a temperature of 104° F (40° C) or higher

Parents should call for any fever in a child who is lethargic, looks ill, or isn't responsive.

When you call the doctor, report 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 prepared to tell your doctor about any symptoms or signs 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 actually 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. Follow the package instructions carefully or the dosing instructions given to you by your health care provider. When given correctly, these medications usually will make the fever go down, although it may not return to normal. If a temperature doesn't respond to fever medication, 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. Give a second dose after 4 to 6 hours, if needed.

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 actually make the temperature go higher. Alcohol baths or wipes should also never be used 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 doctor.