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

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

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

First, wipe down 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). However, 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 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.
  2. If you don't have any of those cleaning products, rinse the sensor in 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 the 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.

Dr. Yacoub recommended the same method you use to sanitize a digital thermometer. 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 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, Stoll advised having separate oral and rectal thermometers (even if the packaging says it's suitable for both uses). You should also label 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, recommended using an antibacterial soap to clean a rectal thermometer. Also, you should ensure that all fecal matter is removed by repeating that process twice.

After cleaning, dry the rectal thermometer with a clean towel, then apply rubbing alcohol. 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." 

When the disinfectant is completely dry, rinse the thermometer with cold water, then wipe it dry with a clean paper towel.

To recap:

  1. Wash the rectal thermometer with antibacterial soap and water twice.
  2. Dry with a clean towel.
  3. Wipe the sensor with a cotton swab or pad dipped in rubbing alcohol or bleach.
  4. Rinse with cold water when completely dry.
  5. 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. 

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 disinfect it when necessary, 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.

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. Dr. Siddiqui said that some thermometers are intended for single use, while others can be disinfected and used multiple times. If your thermometer is disposable, it's not designed to be used again, even if you disinfect it after use.

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