Last Updated on August 30, 2023
We have moved quite a lot from the era of mercury thermometers to a multitude of devices for the measurement of body temperature. Various types of thermometers are now available for measuring body temperature making things more convenient. At the same time, the availability of choice leads to confusion.
Body temperature can be measured from the oral cavity, armpit, ear, rectum, and forehead. Different profiles of patients and different situations may warrant the use of different sites. For example, in very young children rectal temperature is preferred. In other cases, the inability to use the oral cavity may necessitate taking the temperature from the armpit, ear, or forehead.
However, not all sites of measurement are accurate. In fever, we are interested in knowing the core temperature and not just skin temperature. Therefore the rectal temperature followed by the oral cavity provides the most accurate values. However, if these sites have accessibility issues or uncooperative patients, other sites do provide a fair idea if not exact.
Why Different Types of Thermometers?
It would have been good if one type of thermometer could be used at all the places. It would omit many choices and confusion. However because the human body is complex, different anatomic sites for temperature measurement may require varied approaches and therefore different devices. Therefore, we have different types of thermometers.
The latest category addition to types of thermometers is no-contact thermometers. These are based on infrared scans. Forehead scanners have been in immense use for screening purposes during the recent COVID period.
So what is the best type of thermometer for you? Let us discuss.
Different Types of Thermometers
Broadly speaking there are two types of thermometers
Thermometers can also be of two types depending on whether they work by coming into contact with the body or working remotely.
- Contact-based – Those that require body contacts
- No-contact Thermometers – Those which do not require body contact
- Also called remote thermometers
Digital thermometers have replaced, once ubiquitous mercury thermometers.
These types of thermometers have heat sensors to determine the temperature.
Digital thermometers can be used to take temperature readings from
Digital thermometers have the advantage of quick results. These provide the reading in a minute or so.
The rectal temperature provides the most accurate reading especially in cases of infants and children because for oral cavity reading, the tip must be placed under the tongue and the mouth should be closed. That is only possible if one is able to breathe through the nose and is cooperative. The oral temperature should not be immediately taken after consumption of hot or cold stuff as they affect the reading. A wait of 15 minutes is desirable.
Digital thermometers are battery-operated and battery change may be necessary after a period.
For rectal temperature, a dedicated separate thermometer should be used.
Rectal temperatures provide the most accurate readings for infants, especially those 3 months or younger, as well as children up to age 3. Temperatures taken from the armpit are usually the least accurate. For older children and adults, oral readings are usually accurate — as long as the mouth is closed while the thermometer is in place.
This was the only type of thermometer used for taking temperature sometimes back. The use has decreased over the period due to safety concerns.
They consist of mercury encased in a glass. These have safety concerns as glass can break and toxic mercury can escape. These needed to be in place for about 3 minutes.
These can be used in the mouth, rectum, and armpit.
These did not require any power as they were based on mercury expansion.
Contact thermometers are digital/electronic thermometers that require contact with the body. The digital thermometers described above are contact thermometers. These thermometers can be used on the forehead, mouth, armpit, or rectum. Most electronic thermometers have a digital display that shows you the temperature reading.
Most contact thermometers can record temperatures from
The last two options require devices specifically made for that purpose.
Remote or Non-contact Thermometers
Non-contact or remote thermometers do not require contact with the body part for evaluating temperature. They are based on infrared scanning. Therefore, these are very good screening devices at the sites of crowd gathering like airports, schools, theaters, etc.
Remote thermometers while do provide a fair idea are not accurate in the reading.
Temporal Artery/ ForeheadThermometers
It is an infrared scanner to measure the temperature of the temporal artery in the forehead.
The readings are not accurate like oral or rectal but are good enough for screening procedures. The reading can be affected by day temperatures, or a sweaty forehead, and holding distance from the scanner.
These can be used at any age.
The readings are about 1 degree Celsius less than oral readings.
Remote Ear or Tympanic thermometers
These are remote ear thermometers also called tympanic thermometers. These also use an infrared ray to measure ear canal temperature.
These are not recommended for newborns and children less than 6 months of age as the ear canal is shorter.
Earwax or a small, ear canal curvature can affect the reading.
The ear thermometer readings are generally higher by half a degree Celsius.
These can be used in babies for approximate temperature measurement. But they must be in the mouth for at least 6 minutes, unmoved. So they might not add to suitable option for crying babies.
With multiple choices available, it is natural to ask what types of thermometers suit you the best.
The simple digital thermometer is good enough for most people as it allows measurement from multiple sites like the mouth, armpit, and rectum. Combined these options cover most of the age groups.
It is to be kept in mind the accuracy of different sites
- Rectal temperature measurement is the most accurate one
- Oral temperature measurement is typically a 0.5 to 1 degree lower.
- Axillary or armpit measurement is typically 0.5 to 1 degree lower than oral temperatures.
So accordingly, adjustments can be made to the readings.
No-touch, remote thermometers are more useful for screening purposes than individual use. But that does not mean that they cannot be used for that. They can give a fair idea of the situation.
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- Reece RJ, Hughes M. Are Digital Oral Thermometer Readings Accurate in Adult Emergency Department Patients? Cureus. 2022 Feb 9;14(2):e22047. doi: 10.7759/cureus.22047
Pecoraro V, Petri D, Costantino G, Squizzato A, Moja L, Virgili G, Lucenteforte E. The diagnostic accuracy of digital, infrared and mercury-in-glass thermometers in measuring body temperature: a systematic review and network meta-analysis. Intern Emerg Med. 2021 Jun;16(4):1071-1083. doi: 10.1007/s11739-020-02556-0.