Cleaning an oral thermometer takes less than a minute and requires only soap, cool water, and rubbing alcohol. The process is the same whether you just used it on yourself or you’re sharing it between family members, though shared thermometers need the disinfection step every time.
Basic Cleaning With Soap and Water
Start by rinsing the thermometer tip under cool running water. Apply a small amount of liquid soap and gently rub the entire shaft, especially the sensor tip that sits under the tongue. Rinse thoroughly until no soap residue remains. Cool or lukewarm water is important here. Hot water can damage digital thermometer sensors, and some models have plastic components that warp or melt when exposed to high heat. The USDA notes that plastic faces on thermometers can melt in hot liquid, and most thermometers should not be fully immersed in water at all.
This soap-and-water step physically removes saliva, mucus, and most surface bacteria. It’s the minimum you should do after every single use, even if you’re the only person using the thermometer.
Disinfecting With Rubbing Alcohol
After the soap-and-water wash, disinfecting adds a second layer of protection. Soak a cotton ball or cotton pad in rubbing alcohol with at least 60% alcohol concentration. Wipe the entire thermometer tip and shaft thoroughly. The physical action of rubbing the surface is what does much of the work, so don’t just dab it. Let the thermometer air dry completely before putting it away.
This step matters most when the thermometer is shared between people, used during an illness, or hasn’t been cleaned in a while. Improperly cleaned thermometers can harbor serious pathogens. The CDC identifies thermometers as potential vehicles for transmitting C. difficile spores, a bacterium that causes severe intestinal infections and is notoriously hard to kill.
If you don’t have rubbing alcohol on hand, hydrogen peroxide (3% concentration, the standard drugstore bottle) works as an alternative. Apply it the same way, with a soaked cotton ball, and let the thermometer air dry.
Glass Thermometers Need Extra Care
If you still use a glass thermometer, the cleaning process is similar but requires a gentler touch. Wash with soap and cool water, wipe with alcohol, and air dry. Never use hot water on a glass thermometer. Rapid temperature changes can crack the glass, and if the thermometer contains mercury (older models), a break creates a genuine hazard. Mercury produces toxic vapors at room temperature, and those vapors intensify when the liquid is heated.
Most glass thermometers sold today use galinstan (a gallium-based alloy) instead of mercury. If one of these breaks, the liquid inside is far less dangerous. Rinse any exposed skin with water and clean up the spill carefully. Still, preventing breakage through gentle handling during cleaning is the simplest approach.
What Not to Do
A few common shortcuts can ruin your thermometer or give you a false sense of cleanliness:
- Don’t use boiling water. Submerging a digital thermometer in boiling water can melt plastic components, damage the electronic sensor, and void any warranty. It’s unnecessary for the level of disinfection a home thermometer needs.
- Don’t skip drying. Putting a wet thermometer back into a case or drawer creates exactly the environment bacteria love. Moisture draws microorganisms from surrounding air and surfaces, turning your storage case into a breeding ground.
- Don’t just rinse. Running a thermometer under water for two seconds doesn’t remove the bacterial film left by saliva. You need the friction of wiping with soap or alcohol to break that film apart.
- Don’t use bleach or harsh chemicals. These can degrade plastic, corrode metal sensors, and leave residue you’d then put in your mouth.
How to Store It Properly
Once the thermometer is completely air dried, store it in its original protective case or a clean, dry container. Keep it in a drawer or cabinet rather than leaving it out on a bathroom counter, where humidity from showers promotes bacterial growth. The CDC recommends that medical supplies never be stored in locations where they can become wet, since moisture reintroduces microorganisms.
A bathroom medicine cabinet with a door works fine for most households. Avoid storing it loose in a drawer where it can roll around and get contaminated by other items, or where a glass thermometer could crack.
How Often to Clean
Clean your oral thermometer after every use, no exceptions. If multiple family members use the same thermometer during cold and flu season, do the full soap-wash-plus-alcohol routine between each person. Even for a single user, the alcohol step is worth doing when you’re actively sick, since you may be fighting a bacterial infection you’d rather not reintroduce to your mouth days later.
If you pull a thermometer out of storage and can’t remember when you last cleaned it, give it the full treatment before putting it in your mouth. A quick wipe with an alcohol-soaked cotton ball takes about 15 seconds and eliminates any uncertainty.