How to Clean and Store a Thermometer: Simple Steps for Accuracy and Hygiene

The short answer: To clean a thermometer, use rubbing alcohol (70% isopropyl) or soapy water, depending on the type. For digital thermometers, wipe the tip with alcohol and let it air dry. For ear thermometers, gently clean the probe with a soft cloth or cotton swab dipped in alcohol. For mercury glass thermometers, wash with cool soapy water. Always store your thermometer in its case, away from moisture and extreme temperatures, to maintain accuracy and prevent damage.

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Why Proper Cleaning and Storage Matter

Your thermometer is a vital tool for monitoring health, especially when you have a fever. But if it’s not clean, it can spread germs. If it’s not stored correctly, it can give inaccurate readings. A dirty thermometer can also corrode or malfunction, leading to wrong temperatures and potentially dangerous decisions. So, taking a few minutes to clean and store it properly is worth it.

Different thermometers have different cleaning needs. For instance, digital probe thermometers can be wiped with alcohol, but you shouldn’t submerge the entire unit in water. Ear thermometers have delicate sensors that need special care. And mercury thermometers are fragile and require gentle handling. Let’s break it down by type.

Cleaning Digital Probe Thermometers (Oral, Rectal, Underarm)

Digital probe thermometers are the most common. They have a metal or plastic tip that goes in the mouth, rectum, or armpit. Here’s how to clean them:

• Before first use: Clean the probe with a cotton ball or soft cloth dipped in 70% isopropyl alcohol. Let it air dry.
• After each use: Wash the tip with soap and lukewarm water, or wipe it with an alcohol swab. Avoid getting the entire unit wet, especially the electronic parts.
• Deep clean: Once a month, you can disinfect by wiping the probe with a bleach solution (1 part bleach to 9 parts water) for 5 minutes, then rinse and dry. But check the manufacturer’s instructions first.

Do not boil or put in the dishwasher unless the instructions say it’s safe. Heat can damage the electronics.

Cleaning Ear (Tympanic) Thermometers

Ear thermometers are great for kids, but they have a tiny sensor that can be easily damaged. Here’s the safe way to clean:

• Remove the probe cover: If you use disposable covers, just throw the cover away after each use. No cleaning needed.
• Clean the probe: Dip a cotton swab or soft cloth in 70% isopropyl alcohol and gently wipe the tip of the probe. Do not let any liquid get inside the ear canal or the sensor.
• Let it dry: Allow the alcohol to evaporate completely before using it again.
• Avoid water: Never run water over the probe. It can damage the internal components.

If you don’t use covers, clean the tip after every use. Also, clean the lens (the small opening) regularly to remove earwax buildup, which can affect readings.

Cleaning Mercury Glass Thermometers (If You Still Have One)

Mercury thermometers are rare now, but if you have one, handle with care because mercury is toxic. Here’s how to clean them:

• Wash gently: Use cool or lukewarm soapy water and a soft cloth. Do not use hot water, as it can break the glass.
• Never immerse: Only wash the tip, and avoid getting water in the tube.
• Disinfect: Wipe with alcohol after washing, but do not soak.
• Important: If the thermometer breaks, do not touch the mercury. Evacuate the room and call your local health department for cleanup instructions.

For safety, consider replacing mercury thermometers with digital ones. You can find good options in our thermometer buying guide.

Proper Storage for Accuracy and Longevity

Storing your thermometer correctly is just as important as cleaning. Here are the golden rules:

• Always keep it in its protective case: Most thermometers come with a plastic or rubber case. Use it to protect the tip from dust and damage.
• Store in a dry place: Moisture can corrode the sensor and affect accuracy. Avoid bathrooms (often humid) and kitchens (heat and steam). Instead, choose a cool, dry spot like a bedroom drawer or a medicine cabinet.
• Away from extreme temperatures: Don’t leave it in direct sunlight, near a heater, or in a freezing car. Extreme heat or cold can warp the electronics and cause inaccurate readings.
• Keep out of reach of children: Thermometers are not toys. Store them in a locked cabinet if you have young kids.

For travel, use a hard case if possible to prevent damage.

How to Maintain Accuracy Over Time

Thermometers can drift out of calibration, especially after rough handling or exposure to extreme conditions. Here’s how to keep yours accurate:

• Check with an ice bath: For probe thermometers, you can test accuracy by placing the tip in an ice water mixture (32°F or 0°C). It should read around that temperature. If it’s off by more than 0.5°F, it may need recalibration (if it has a reset button) or replacement.
• Follow manufacturer’s guidelines: Some thermometers specify a calibration period. Replace batteries regularly, as low battery can affect readings.
• Clean before each use: Dirt and oils can insulate the sensor, giving lower readings.

If your thermometer is consistently off, it’s time for a new one. Check out our recommended thermometers for reliable options.

Common Mistakes to Avoid When Cleaning and Storing Your Thermometer

Even with good intentions, some habits can shorten your thermometer’s life or compromise hygiene. Here are the most frequent errors and how to steer clear of them.

• Submerging the entire digital unit: Water can seep into the battery compartment and circuitry, causing corrosion or short circuits. Only the probe tip should get wet, and even then, keep the display and buttons dry.
• Using harsh chemicals: Bleach, ammonia, and other strong cleaners can degrade plastic and rubber parts, and leave residues that irritate mucous membranes. Stick to 70% isopropyl alcohol or mild soap.
• Cleaning while hot or cold: If you just took a reading, the probe may be at body temperature. Sudden temperature changes from cold water or alcohol can stress the sensor. Let it return to room temperature first.
• Storing in the bathroom: The humidity from showers can cause mold growth on the case and corrode metal contacts. A bedroom drawer is a better choice.
• Forgetting the probe cover: For ear thermometers, reusing a cover or skipping it altogether can transfer earwax and bacteria. Always use a fresh cover for each user.
• Ignoring the battery compartment: Leaking batteries can destroy a thermometer. Remove batteries if you won’t use it for months, and check for corrosion regularly.

By avoiding these pitfalls, you’ll keep your thermometer in top shape and ensure reliable readings when you need them most.

How to Choose the Right Thermometer for Your Needs

If you’re in the market for a new thermometer, the cleaning and storage requirements should factor into your decision. Here’s what to consider for different types.

• Digital probe thermometers: These are versatile and generally easy to clean. Look for models with a waterproof tip (not the whole unit) and a flexible tip for comfort. They work for oral, rectal, and underarm use, but you’ll need to label them if you use the same one for different sites.
• Ear thermometers: Convenient for kids and fast, but they require probe covers to stay hygienic. Check that replacement covers are easy to find and affordable. Some models have a pre-warmed tip to improve accuracy.
• Forehead (temporal artery) thermometers: These are non-invasive and don’t require probe covers, but the sensor lens needs regular cleaning to remove skin oils and dust. They’re a good option for sleeping children.
• Infrared no-touch thermometers: Great for avoiding contact, but the sensor can be affected by environmental factors like drafts and direct sunlight. They need minimal cleaning, just a wipe of the lens.
• Smart thermometers: These connect to apps and may have specific cleaning instructions. Usually, the probe is cleaned like a digital one, but avoid getting the body wet.

Consider who will use it and where. For a household with multiple users, a digital probe with disposable covers or an ear thermometer with covers might be most hygienic. For travel, a compact digital model with a hard case is ideal.

When to Replace Your Thermometer

Even with perfect care, thermometers don’t last forever. Knowing when to replace yours ensures you’re not relying on faulty readings.

• Inconsistent readings: If you get wildly different temperatures within minutes, or if readings don’t match how the person feels, it may be time for a new one.
• Physical damage: Cracks in the probe, a cracked display, or a loose battery cover can let in moisture and cause malfunctions.
• Calibration drift: If your ice bath test shows an error greater than 0.5°F (0.3°C) and there’s no way to recalibrate, replace it.
• Battery issues: If the thermometer frequently needs new batteries or won’t turn on, the electronics may be failing.
• After a contagious illness: While thorough cleaning can disinfect, some experts recommend replacing a thermometer after a serious illness like COVID-19 if it was used orally or rectally and cannot be fully disinfected.
• Outdated technology: Mercury thermometers should be replaced with digital ones for safety and accuracy.

Typically, a well-cared-for digital thermometer can last several years. But if you notice any of the above signs, it’s better to replace it than risk a wrong reading.

Frequently Asked Questions

Can I clean a thermometer with boiling water?

No, unless the manufacturer explicitly says it’s safe. Boiling can damage digital sensors and cause mercury thermometers to break. Use alcohol or soapy water instead.

How often should I clean my thermometer?

Clean it before and after every use, especially if it’s shared. For home use, a quick alcohol wipe after each use is sufficient. Deep clean once a month.

What is the best way to store a thermometer?

In its case, in a dry, cool place away from direct sunlight and moisture. Avoid bathrooms and kitchens.

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