Types of thermometers

A thermometer is a device that is used to measure the body temperature. These days, with advancing medical technology, thermometers are available that of different kinds and varying accuracies. In this article, we shall briefly review the types of thermometers that are currently available on the market that are used to measure body temperature in patients who are ill.

1. The traditional mercury thermometer

The traditional thermometer is a small pencil shaped instrument with a mercury filled bulb and a thin glass column placed within a glass body that is graduated with both Fahrenheit and Celsius readings. When placed either in the oral cavity or in the armpit, the temperature causes the mercury to rise to the column until the final reading on the barometer corresponds to the body temperature.

The main advantage of the traditional thermometer is that it requires very little maintenance. Once utilised, it can be easily cleaned using antiseptic solution and water and reused. However, the accuracy of the traditional thermometer has been questioned, with some stating that it could be unreliable. This is partly related to the way the patient’s place the thermometer in their mouth and also the way the health care professional reads the mercury column.

Nonetheless, the traditional thermometer is still widely used all over the world in numerous hospitals and in clinic settings.

2. Digital thermometers

A digital thermometer is a recent introduction into the field of medicine. It works on the principle of recording body temperature through the mouth, armpit or the rectum (bottom) using a device that has electronic heat sensors at the tip. It is an excellent way to check temperature in extremely ill patients and in children.

Digital thermometers are typically used through the rectum in infants as this can measure what is known as the ‘core body temperature’. As children get older, oral temperatures can be recorded with greater degree of accuracy. However, accuracy depends upon where the thermometer is positioned within the mouth and also on the fact that the mouth is closed completely.

One of the prime the advantages of digital thermometers is that it can record the temperature extremely quickly. However, the thought of having temperature checked regularly can be put off the some patients or the parents of infants and children.

3. Forehead thermometers

These are also a relatively new kind of thermometers that measure the temperature of the skin on the forehead. They work by getting heat when the thermometer is placed over the temple. Unfortunately, while the use of the thermometer is extremely easy, it can in fact be slightly unreliable as a degree of error is noted when the temperature is checked.

4. Electronic ear thermometers

This thermometer measures the temperature in the inside of the ear. It is also sometimes called a tympanic thermometer. The thermometer is placed inside the ear and detects infrared heat within the ear. The primary advantage of using electronic ear thermometers is that it is simple to use, quick to record the body temperature and is quite reliable. However, in situations where there is a very high ear wax content, recording from the electronic ear thermometers may not necessarily be reliable. Furthermore, the use of electronic ear thermometers in infants and small children may not yield accurate results.

5. Pacifier thermometer

A pacifier thermometer is used in the measurement of temperature in babies over the age of three months. A small pacifier has an electronic heat recorder at the tip of it that is used to measure body temperature. In order for this pacifier thermometer to be used accurately, it should be placed in the mouth of the child for a few minutes at least. Many a time, children who are moving around or very small children may not be willing to keep the thermometer in the mouth which makes it difficult to record temperature accurately. However, many children do not realise that the pacifier is actually a thermometer and may well keep them in the mouth, allowing for a reasonably accurate temperature measurement.

6. Temperature strips

Also called plastic fever strip thermometers, these thermometers contain on them liquid crystals that are sensitive to heat and change colour when in contact with a hot surface. While they are fairly simple to use in theory, in practice they can be highly unreliable. This is because the colour on the temperature strips may vary depending upon the surrounding environmental temperature.

Choosing the right thermometer

In infants and in children, using a digital thermometer is probably the most accurate way of measuring body temperature. Tympanic thermometers are also excellent and can be used with similar accuracy. Avoiding temperature strips and mercury thermometers is strongly recommended in infants and children.

In adults, these days’ tympanic thermometers and digital thermometers are being used more and more. This is primarily due to their efficacy but also due to the fact that not many patients like having mercury thermometers placed in their mouth to check the temperature. This is because of increased awareness of the dangers of mercury.


Thermometers are of numerous kinds. With advanced technology, using digital thermometers and tympanic thermometers has now come into vogue over and above the usual mercury thermometers that were used many years ago. Accuracy has improved tremendously with temperatures being recorded to the first decimal point. Temperature can also be recorded through hygienic methods especially with the forehead thermometers and tympanic thermometers (a removable casing is placed on top each time the thermometer is used). Obtaining an accurate temperature recording can help guide appropriate management strategies.

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