The Different Types Of Thermometers And How To Use Them

By Tiffany Tseng. May 7th 2016

When you or someone you love has a fever for the first time, the variety of thermometers may seem to be confusing and overwhelming. Here is a guide to basic thermometers used for medical purposes.

Electronic Thermometers

  • Digital heat sensor: these are standard electronic thermometers, and use electronic heat sensors to detect body temperature. These thermometers can be used in the mouth, armpit or rectum. Sometimes, it can come in the form of a pacifier for infants who cannot keep still when having their temperature measured. When in doubt, invest in a digital heat sensor thermometer, as it is appropriate for all ages and is very accurate.
  • Infrared wave sensor: these thermometers use infrared rays to measure the body’s temperature. The most common form is the ear thermometer, also referred to as the tympanic thermometer. A new and developing thermometer that measures the temporal artery in the forehead also uses infrared waves to measure temperature.
  • Basal thermometers: these thermometers are a form of digital thermometer that is highly sensitive and tracks precise, minute, temperature changes within the body. They are most often used for female fertility purposes and ovulation tracking rather than general, body temperature measuring purposes. A normal thermometer usually measures temperature in two-tenths of a degree increments, while a basal thermometer measures by tenths of a degree.

Liquid-Filled Glass Thermometers

  • Mercury filled: mercury thermometers used to be the household item for measuring body temperatures, but according to US News, it has been phased out for commercial use. If the thermometer is accidentally broken, the liquid and the fumes it emits are extremely toxic to both humans and the environment. If you still have mercury thermometers at home, be sure to contact your local recycling center for safe and proper ways to dispose the thermometer.
  • Alcohol filled: for those who wish to keep using liquid filled thermometers over electronic ones, alcohol-filled thermometers are the standard replacement for mercury ones. The alcohol is infused with a dye, so it can be easily read and is not toxic to the environment if accidentally broken. This thermometer measures temperature via thermal expansion of the ethanol, and should be held in place for several minutes until the expansion stops. To reset the thermometer, be sure to shake it until the alcohol level resumes to room temperature before using it again.

Other Types of Thermometers

  • Temperature strips: although not exactly a thermometer, temperature strips still measure the body’s temperature due to liquid crystals that react to heat. It is usually placed against the forehead and changes color, which can be matched to a provided chart to estimate a person’s temperature. However, it is largely inaccurate as environmental heat can also influence color change. Opt for a digital thermometer instead if you have the option to.

Tips On Using Thermometers

  • The most accurate way to measure an infant’s temperature is rectally with a digital thermometer.
  • Measuring body temperature through the armpit is probably the most inaccurate, in comparison to oral or rectal measurements.
  • Invest in two thermometers, one for oral measurement and one for rectal measurements. Do not use one thermometer only for both purposes.
  • Ear thermometers are not recommended for infants, as earwax buildup or a curved, tiny ear canal may yield inconsistent temperature readings.
  • If taking the temperature orally, do not move the mouth around and make sure the thermometer is in one place, under the tongue. Also, do not open the mouth until the temperature is verified.
  • If taking the temperature orally, wait at least 15 minutes after food or beverage consumption before measuring for accuracy.
  • If body temperature needs to be recorded over a period of time, it is best to take the temperature at the same time everyday with the same thermometer for optimal comparison. This is especially important when using basal thermometers for female fertility purposes.
  • Before using the thermometer, make sure the contact tip of the mechanism, as well as the intended contact surface, are clean and debris free. It doesn’t hurt to wipe both with some rubbing alcohol, just in case, before use.

How To Take Care Of Your Thermometer

Regardless of the type of thermometer you choose to use, it is important to follow the instructions enclosed with the packet upon purchase for optimal results and product longevity. For regular digital thermometers and alcohol-filled thermometers, be sure to sterilize the tip with rubbing alcohol, or wash well with warm water and soap after each use. For ear or tympanic thermometers, it may be helpful to invest in some disposable caps that can be tossed after each use. Store all thermometers with the rest of your first aid supply, and keep away from children and infants for their safety as thermometers are not toys.


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