How To Disinfect a Thermometer and When You Need To Do It

A thermometer is essential in every home medical kit, as fever is a symptom of many contagious viruses and infections.

But it's essential to keep your thermometer clean to avoid spreading germs between family members. 

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

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

Before Disinfecting a Thermometer

Before disinfecting and using a thermometer, ensure you wash your hands with soap and water or disinfect them with hand sanitizer, said Stoll. But if your hands are visibly dirty, choose the soap and water option.

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

How To Clean and Disinfect a Digital Thermometer

Digital thermometers are the most common type of thermometer that is used. To clean and disinfect a digital thermometer, first, wipe your digital thermometer with a cotton swab dipped in rubbing alcohol, said Stoll. Rubbing alcohol with an alcohol level of 60% or higher is most effective at killing bacteria.

Some evidence suggests that alcohols—specifically isopropyl alcohol and ethyl alcohol (ethanol)—can inactivate a broad spectrum of bacteria, fungi, and viruses. Those alcohols play a vital role in disinfecting small medical tools in the healthcare industry. 

"The action of rubbing the surface of the thermometer helps to disinfect," explained Stoll. And if you don't have rubbing alcohol, use a bleach wipe instead.

Take care not to submerge the digital part of the thermometer in fluid. Water and electronic components don't mix well, and water can damage the digital components of the thermometer. Instead, wipe the display screen with a damp cloth.

However, the tip can be rinsed in lukewarm soapy water if desired. Soap will clean any germs off the thermometer. But make sure not to use hot water, which can damage the sensor.

Finally, always leave it to air dry before putting it into storage. Bacteria thrive in warm, moist environments, so letting the thermometer properly dry will kill any germs.

Get into the habit of repeating those every time the same thermometer is used by two different people or used by the same person after a long time.

To recap:

1. Wipe the sensor with a cotton swab or pad dipped in rubbing alcohol or bleach. Be careful to avoid the display screen and other digital parts.
2. If you don't have any of those cleaning products, rinse the sensor in lukewarm soapy water.
3. Let the digital thermometer air dry.
   

How To Clean and Disinfect a Forehead Thermometer

A temporal artery, or forehead, thermometer is used externally, measuring infrared heat waves from a large blood vessel that runs across the forehead just below the skin. 

Some of those thermometers don't come into direct contact with the skin. However, it would be best if you still sanitized them before and after each use, Ramzi Yacoub, PharmD, chief pharmacy officer at SingleCare, told Health.

Use the same method you use to sanitize a digital thermometer, said Dr. Yacoub. Soak a cotton ball or pad with rubbing alcohol of at least 60% alcohol volume, or use a bleach wipe. Again, give the thermometer time to air dry before putting it back into storage.

To recap:

1. Wipe the sensor with a cotton swab or pad dipped in rubbing alcohol or bleach. Or, you can rinse the forehead thermometer with lukewarm soapy water.
2. Let the forehead thermometer air dry.
   

How To Clean and Disinfect a Rectal Thermometer

Rectal thermometers (inserted into the anus) are the most accurate and recommended for children up to age four.

"Both oral and rectal thermometers touch a person's mucus membranes, so it's very important to disinfect well," noted Stoll. 

Additionally, have separate oral and rectal thermometers (even if the packaging says it's suitable for both uses), advised Stoll. You should also label them to avoid accidentally using a rectal thermometer in the mouth.

Ensure that you're using an antibacterial soap to clean a rectal thermometer, California-based infectious disease specialist Javeed Siddiqui, MD, MPH, co-founder and chief medical officer at telemedicine company TeleMed2U, told Health. Repeat that process twice to remove all fecal matter.

After cleaning, apply rubbing alcohol or bleach with a cotton swab or pad. Also, check the thermometer manufacturer's guidelines, as they might recommend a particular type of disinfectant. Those may include an iodine or glutaraldehyde solution.

"It's critically important that the disinfectant be allowed to dry," said Dr. Siddiqui. "This drying process allows for appropriate disinfection." 

To recap:

1. Wash the rectal thermometer with antibacterial soap and lukewarm soapy water twice.
2. Dry with a clean paper towel.
3. Wipe the sensor with a cotton swab or pad dipped in rubbing alcohol or bleach.
4. Wipe dry with a clean paper towel.

How To Clean and Disinfect an Ear Thermometer

An ear thermometer has a tiny sensor inserted into the ear canal to measure temperature. You can buy disposable covers or caps to put over the sensor. But keep in mind: Ear thermometers are not accurate in children less than six months old.

Still, if you don't have those, keep your ear thermometer clean by wiping the sensor with a cotton swab or pad dipped in rubbing alcohol—of at least 60% alcohol volume—or a bleach wipe, and let it dry, said Yacoub. 

You can also wipe the thermometer's body with a slightly damp cloth, but ensure you don't submerge it in water, as that could damage the device.

To recap:

1. Wipe the sensor with a cotton swab or pad dipped in rubbing alcohol or bleach. Be careful to avoid submerging the ear thermometer in water.
2. Let the ear thermometer air dry.
   

Can Multiple People Use the Same Thermometer?

The best practice is to have a separate thermometer for each household member, noted Stoll. But if that's not possible, multiple people can use the same thermometer, provided you clean and disinfect between uses, added Yacoub. 

It's important to disinfect your thermometers before and after each use, even if the body temperature reading is regular. An average body temperature varies by person, age, and time of day but is generally accepted to be 98.6 degrees Fahrenheit (which is 37 degrees Celsius).

A Quick Review

Disinfecting a thermometer is particularly important for children because they are more susceptible to sharing and spreading germs, Chelsea Johnson, MD, associate lead of pediatrics at K Health, told Health.

Before using a thermometer, it's essential 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 used multiple times, added Dr. Siddiqui. If your thermometer is disposable, it's not designed to be used again, even if you disinfect it after use.