Cleaning a thermometer takes less than a minute: wipe the probe or tip with rubbing alcohol (60% to 90% isopropyl or ethyl alcohol), let it air dry, and store it in a clean case. That basic routine kills the bacteria most likely to spread between uses. The details vary slightly depending on what type of thermometer you own, so here’s what to do for each.
Why Alcohol Works Best
Rubbing alcohol in the 60% to 90% range is the gold standard for disinfecting thermometers at home. According to the CDC, alcohols in that concentration range kill common bacteria like Staph, Strep, E. coli, and Salmonella in as little as 10 seconds of contact. Below 50%, the germ-killing ability drops sharply, so don’t water it down.
The standard 70% isopropyl alcohol you find at any pharmacy is ideal. It’s cheap, evaporates quickly, and won’t damage the plastic or metal on most thermometers. Soap and cool water also work as a first-pass cleaning step, but following up with alcohol gives you a more reliable disinfection.
Cleaning a Digital Oral Thermometer
Digital stick thermometers are the most common type in households, and they’re the simplest to clean. Here’s the process:
- Before each use: Wipe the metal probe tip with a cotton ball or pad soaked in rubbing alcohol. Alternatively, wash the tip with soap and cool water, then rinse thoroughly.
- After each use: Repeat the same step. Wipe down the probe with alcohol or wash with soap and water, then let it air dry completely before putting it away.
Avoid using hot water. It can damage the sensor inside the tip and warp plastic housing. Cool or lukewarm water is all you need for the soap-and-water method. Also avoid submerging the entire thermometer unless the manufacturer says it’s waterproof. Many digital thermometers are only water-resistant around the tip, not the battery compartment or display end. If your thermometer has an IP67 rating (check the packaging or manual), it can handle full submersion. Otherwise, keep the body of the unit dry and focus your cleaning on the probe.
Cleaning a Rectal Thermometer
Rectal thermometers need more careful attention because of the bacteria involved. Clean the probe with rubbing alcohol after every single use, and again before the next use. Some families designate a specific thermometer for rectal readings only. If you do this, label it clearly so it never gets mixed up with an oral thermometer.
The cleaning steps are the same as for an oral thermometer: wipe the probe thoroughly with an alcohol-soaked cotton pad, making sure to cover the entire surface that made contact. Let it dry fully before storing. If you use disposable probe covers, you still need to clean the thermometer itself afterward. Covers can tear, shift, or allow small amounts of contamination to reach the probe underneath.
Cleaning an Infrared or Non-Contact Thermometer
Infrared thermometers, including forehead scanners and ear thermometers, have a sensor lens instead of a metal probe. This lens is more delicate than it looks, and scratching it will throw off your readings.
Don’t wipe the lens with a cloth, paper towel, or household cleaning wipe. Instead, dip a cotton swab in isopropyl alcohol and gently clean the lens surface. This removes dust, skin oils, and any debris without scratching the optic. For the outer housing, a soft cloth dampened with alcohol or soapy water works fine. Just keep liquid away from the lens area unless you’re using the cotton swab method.
Ear thermometers often come with disposable lens covers. Replace these after each use. Even with covers, give the lens an occasional cleaning with the cotton swab technique to keep readings accurate.
Cleaning a Glass Thermometer
If you still use a glass thermometer (the non-mercury, galinstan type), the cleaning process is straightforward. Wash the entire thermometer with cool, soapy water, rinse it well, then wipe it down with rubbing alcohol. Glass can handle full submersion, so you don’t need to worry about water damage.
Be gentle. Glass thermometers are fragile, and dropping one on a tile floor means shards and cleanup. Dry it with a soft cloth rather than shaking it over a hard surface.
Drying and Storage
Always let your thermometer dry completely before putting it away. Trapping moisture inside a case creates exactly the kind of warm, damp environment where bacteria grow. Alcohol evaporates quickly on its own, usually within 30 seconds to a minute, so a brief wait is all it takes.
Store thermometers in their original protective case or a clean, dry container. Keep them away from direct sunlight and extreme temperatures, both of which can affect sensor accuracy over time. If your thermometer uses a button battery, storing it wet or damp can also cause corrosion around the battery contacts.
How Often to Clean
The short answer: every time you use it, both before and after. This matters most when a thermometer is shared between family members, but it applies even if you’re the only one using it. Your mouth, ear canal, and skin all carry bacteria that can colonize a thermometer surface between uses. A quick alcohol wipe takes seconds and eliminates the risk.
If a thermometer has been sitting in a drawer untouched for months, clean it before you trust it against your body. Dust, residue from previous use, and general household grime can all accumulate. Give it the standard alcohol wipe, let it dry, and it’s ready to go.