What Are the Different Types of Thermometers, and How Do You Use Them?
Medically Reviewed by Carolin Schneider, MD
Thermometers are healthcare devices you can use to take your or another person’s temperature. There’s a variety of thermometers to choose from, and each can work best for different applications and provide different levels of accuracy.
If you’re in need of a new thermometer, there are a few important things to consider that can help guide you in the selection process. The thermometer’s placement, the ease of reading it and the age of the person whose temperature you need to take are all factors that can help you in deciding which thermometer is best for your needs.
Digital Heat Sensor: These are standard electronic thermometers and use electronic heat sensors to detect body temperatures. You can use these thermometers in your mouth, armpit or rectum. They’re appropriate for all ages and are very accurate.
Infrared Wave Sensor: These thermometers use invisible infrared rays to measure your body’s temperature. Ear (also known as tympanic) thermometers and forehead (also known as temporal artery) thermometers are the most common. They’re beneficial if you need to keep distance between yourself and the person whose temperature you’re taking.
Basal Thermometers: These digital thermometers are highly sensitive and track precise temperature changes within your body. A normal thermometer usually measures temperatures in increments of two-tenths of a degree increments. However, a basal thermometer measures by tenths of a degree. People often use them for fertility purposes and ovulation tracking rather than general body temperature-measuring purposes.
Liquid-Filled Glass and Other Thermometers
Mercury Filled: Mercury thermometers were once common, but healthcare professionals advise against using them now. They’re made of glass tubes with smaller tubes inside filled with mercury. Mercury is toxic, and these thermometers can be harmful if you break the tube. Instead of throwing a mercury thermometer in the trash, contact your local trash or recycling center to learn about ways to properly dispose of it.
Alcohol Filled: If you prefer to use liquid-filled thermometers over electronic ones, alcohol-filled thermometers are a safer alternative to mercury. The alcohol is infused with a dye, so the measurement is easy to read and isn’t toxic to the environment if you accidentally break the thermometer. This thermometer measures your temperature when heat causes the alcohol inside the thermometer tube to expand. Make sure to check what kind of thermometer it is to ensure you’re placing it correctly. To reset the thermometer, shake it until the alcohol level returns to room temperature before using it again.
Temperature Strips: Although they’re not exactly a thermometer, temperature strips still measure your body’s temperature. They do this using liquid crystals that react to heat. You can place them against your forehead, and they change color. You’ll match the color to a chart that’s provided with the strips to estimate your temperature. These strips aren’t very accurate because ambient heat in the air around you can cause color changes.
Tips on Using Thermometers
There are some other reasons that certain thermometers may be more or less useful to you. Here are some extra tips to follow for choosing and using a thermometer:
- The most accurate way to measure an infant’s temperature is rectally with a digital thermometer, especially if they’re younger than 3 months old. Use petroleum jelly on the tip of the thermometer.
- Oral and rectal measurements are more accurate than armpit and forehead measurements.
- Invest in two thermometers — one for oral measurements and one for rectal measurements. Do not use one thermometer for both purposes.
- Ear thermometers aren’t recommended for infants. Earwax buildup or the baby’s curved, tiny ear canal can provide inconsistent temperature readings.
- If you’re taking your temperature orally, don’t move your mouth around. Make sure the thermometer is in one place under your tongue. Keep your mouth closed until you’re done taking the reading.
- If you’re taking your temperature orally, wait 15–30 minutes after eating or drinking for the most accurate results.
- If you need to record your body temperature at different points over a period of time, it’s best to take your temperature at the same time every day with the same thermometer. This gives you the most accurate numbers.
- Before using the thermometer, make sure the contact tip is clean and debris free. It doesn’t hurt to wipe it with some rubbing alcohol just in case before use. Be sure to let the alcohol evaporate before using it, especially if you’re inserting the thermometer orally.
- Temperatures can change during the day due to the environment and activities you’re doing. Some medications can lower your temperature as well.
Taking Care of Your Thermometer
Whatever type of thermometer you choose to use, it’s important to follow the instructions enclosed with its packaging to get the best results and to ensure you don’t damage the device. For contact thermometers, be sure to sterilize the tip with rubbing alcohol or wash it well with warm water and soap after each use. For ear or tympanic thermometers, it may be helpful to invest in some disposable caps you can throw out after each use. Store all thermometers with the rest of your first aid supplies, and keep them away from kids.
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“Temperature: Digital and Glass Thermometers,” Nationwide Children’s