How to Clean a Thermometer

From seasonal influenza to COVID-19, many contagious viruses manifest with fevers. Thermometers help determine whether your child has an elevated temperature, but did you know that dirty ones can spread disease-causing bacteria between members of your household?

"If the thermometer is being used on the same person each time, there is no need for sterilization," explains Robert Frenck, M.D., Medical Director, Division of Infectious Diseases at Cincinnati Children's Hospital. But if it's used on multiple people, you should take measures to kill germs and bacteria before each use—even if everyone's temperature reads normal.

Here's how to clean and sanitize four types of thermometers: digital, rectal, forehead, and ear.

Digital Thermometers

"If you're using a digital thermometer, it's best to wipe the thermometer down with rubbing alcohol or a bleach wipe and let the thermometer dry," says Dr. Frenck. Here are the steps for disinfecting a digital thermometer:

1. Choose a rubbing alcohol with at least 60% alcohol, since that's most effective at killing bacteria, according to the Centers for Disease Control and Prevention (CDC). Dowse a cotton pad or ball with rubbing alcohol. You can also grab a bleach wipe.
2. Coat the entire body of the thermometer with the disinfectant solution, making sure to rub it in thoroughly.
3. Rinse the thermometer in cool running water to eliminate traces of alcohol. Avoid wetting the digital components, such as the display. If you want to clean these parts, wipe them with a damp cloth.
4. Let the digital thermometer air dry before putting away. Wiping with a towel could reintroduce bacteria.

As an alternative, you can use soap and water. But again, you shouldn't submerge the digital components, since this could damage the device, says Dr. Frenck.

Rectal Thermometers

You'll probably choose a rectal thermometer before your child turns 3. Use the rubbing alcohol method outlined above for digital thermometers (although soap and water works too, as long as you don't submerge the device). Make sure to clean rectal thermometers before and after using.

Also, to be safe, you shouldn't use the same thermometer rectally and orally, even if the packaging says you can use it both ways, says Jennifer Shu, M.D., coauthor of Heading Home with Your Newborn: From Birth to Reality. Label the one you only use rectally so that you don't make a mistake.

Infrared or Forehead Thermometers

These thermometers gauge temperature externally—usually on the forehead—and they're a great option for those with finicky children. Some products work without directly touching the skin, but you should still sanitize them before and after each use. Clean the sensor with a cotton ball or pad soaked with rubbing alcohol; it should have at least 60% alcohol volume. Bleach or alcohol wipes also work. Let the thermometer dry before putting it away.

Ear Thermometers

As the name suggests, ear thermometers are inserted into the ear canal to read temperature. Wipe the tiny sensor with a cotton swab dipped in rubbing alcohol, and then let dry. You can also wipe the body of the thermometer with a slightly damp cloth—but again, you should avoid submerging in water to prevent damage.