Thermometers can harbor bacteria and transmit infection if not properly disinfected.

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A thermometer is an essential item in every home medical kit—and given that fever is one of the most common COVID-19 symptoms, you might have used yours more frequently than usual due to the pandemic. But it's important to keep your thermometer clean so you avoid spreading germs between family members.

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"Thermometers can potentially harbor bacteria and transmit infection," Tracey Stoll, RN, manager of infection prevention at Santa Clara Valley Medical Center in San Jose, California, tells Health. "By cleaning the thermometer every time, both before and after use, you are reducing the risk of infection."

Here's how to disinfect your thermometer between uses to help keep everyone in the home healthy.

Before disinfecting a thermometer

Before disinfecting and using a thermometer, make sure you wash your hands with soap and water or disinfect them with hand sanitizer, Stoll says. (If your hands are visibly dirty, you should go for the soap and water option, she adds.)

Only when your hands are clean should you start the disinfection process.

How to disinfect a digital thermometer

First, wipe down your digital thermometer with a cotton swab dipped in rubbing alcohol, Stoll says. (Rubbing alcohol with an alcohol level of 60% or higher is most effective at killing bacteria, according to the Centers for Disease Control and Prevention.) If you don't have rubbing alcohol, use a bleach wipe instead.

"The action of rubbing the surface of the thermometer helps to disinfect," Stoll explains. Take care not to submerge the digital part of the thermometer in fluid (water and electronic components don't mix well), though the tip can be rinsed in water if desired. Finally, always leave it to air dry before putting it into storage.

Get into the habit of doing this every time the same thermometer is used by two different people and/or used by the same person after a long time.

How to disinfect a forehead thermometer

A temporal artery thermometer is used externally, measuring infrared heat waves coming off the blood vessel that runs across the forehead just below the skin. Some of these thermometers don't actually come into direct contact with the skin, but they should still be sanitized before and after each use, Ramzi Yacoub, PharmD, the chief pharmacy officer at SingleCare, tells Health.

He recommends the same method you use to sanitize a digital thermometer: Soak a cotton ball or pad with rubbing alcohol that has at least 60% alcohol volume, or use a bleach wipe. Again, give the thermometer time to air dry before putting it back into storage.

How to disinfect a rectal thermometer

The American Academy of Pediatrics says rectal thermometers (inserted into the anus) are the most accurate and recommends them for use on children up to age 4 years.

"Both oral and rectal thermometers touch a person's mucus membranes, so it's very important to disinfect well," Stoll says. She advises having separate oral and rectal thermometers (even if the packaging says it's suitable for both uses), and labelling them to avoid accidentally using a rectal thermometer in the mouth.

California-based infectious disease specialist Javeed Siddiqui, MD, MPH, co-founder and chief medical officer at telemedicine company TeleMed2U, recommends using an anti-bacterial soap to clean a rectal thermometer, making certain that all fecal matter is removed (he suggests doing this twice, to be extra sure). After cleaning, dry the rectal thermometer with a clean towel, then apply rubbing alcohol. It's a good idea to also check the thermometer manufacturer's guidelines, as they might recommend a particular type of disinfectant, such as an iodine or glutaraldehyde solution.

"It's critically important that the disinfectant be allowed to dry," Dr. Siddiqui says. "This drying process allows for appropriate disinfection." When the disinfectant is completely dry, rinse the thermometer with cold water, then wipe it dry with a clean paper towel.

How to disinfect an ear thermometer

An ear thermometer has a tiny sensor that's inserted into the ear canal to measure temperature. You can buy disposable covers or caps to put over the sensor, but if you don't have these, you can keep it clean between uses by wiping the sensor with a cotton swab or pad dipped in rubbing alcohol (at least 60% alcohol volume—you know the drill) or a bleach wipe, and let it dry, Yacoub says. You can also wipe the body of the thermometer with a slightly damp cloth, but make sure you don't submerge it in water, as this could damage the device.

Can multiple people use the same thermometer?

Stoll says that the best practice is to have a separate thermometer for each member of a household. But if that's not possible, then yes, multiple people can use the same thermometer—provided you disinfect it when necessary, Yacoub says. He emphasizes that it's important to do this before and after each use even if the body temperature reading is normal (this varies by person, age, and time of day, but is generally accepted to be 98.6 degrees Fahrenheit).

Disinfecting a thermometer is particularly important when it's used on children because they are more susceptible to sharing and spreading germs, Chelsea Johnson, MD, FAAP, from digital primary care platform K Health, tells Health.

Before using a thermometer, it's important to check the manufacturer's recommendations and guidelines, according to Dr. Siddiqui. Some thermometers are intended for single use, while others can be disinfected and uses multiple times, he says. If your thermometer is the disposable sort, it's not designed to be used again, even if you disinfect it after use.

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