Thermometry is the measurement of temperature. A medical thermometer is a device used to measure and monitor body temperature. They are available as contact or non-contact devices. An elevated temperature in children is one of the primary reasons why a parent will contact their medical professional so a thermometer is an essential part of your first aid kit. Understanding the types of thermometers available will help you choose the most suitable option for your family. Readings and accuracy vary according to the type of thermometer you use, so consider your reasons for purchasing a thermometer and bear in mind the ages and stages of your family members when choosing your device. 

Scales of measurement

There are two scales of measurement used to observe body temperature, the Celsius scale, also known as centigrade, and the Fahrenheit scale. Normal human body temperature varies between 36–37°C or 98–100°F. Some thermometers will provide the option of both scales. 

A fever is an increase in body temperature above the normal range of 36–37°C (98–100°F) and is the body’s natural response to infection or illness. A decrease in body temperature can also be an indicator of ill health. 

Technique and temperature variations 

Body temperature can be measured by 4 different methods:

Under the armpit - axillary method

In the mouth - oral method

In the ear - tympanic method

In the rectum - rectal method

It is important to note that temperature readings will vary according to the method used and the correct use of your thermometer. Rectal thermometers provide the most accurate reading of body temperature. 

Method Normal temperature range

Armpit           36.5°C - 37.5°C (97.8°F - 99.5°F)

Mouth           35.5°C - 37.5°C (95.9°F - 99.5°F)

Ear           35.8°C - 38°C (96.4°F - 100.4°F)

Rectal            36.6°C - 38°C (97.9°F - 100.4°F)

Body temperature can fluctuate throughout the day. It is generally at its lowest when we wake in the morning after a long period of rest, but can rise by as much as 1 degree by late morning and peak at the top of the normal range by late afternoon. Exercising, being outdoors on a hot sunny day or too many layers of clothing can also cause mild fluctuations in temperature. 

Types of thermometer

In times past we were familiar with the traditional glass and mercury thermometers. They were versatile but delicate and were removed long ago from routine home and medical use due to the potential for mercury exposure. Mercury is a powerful neurotoxin. We now have a range of safe and convenient medical thermometers available to us, which we will explore below.

In the light of the Covid-19 pandemic, non-contact infrared thermometers have become indispensable for temperature screening, both at home and in public settings.

Strip thermometers, while inexpensive to buy and simple to use, can be inaccurate as they measure the temperature of the skin on the forehead and not body temperature and will not be otherwise mentioned in this article. 

Infrared Forehead Thermometers (Temporal)

Forehead thermometers use infrared sensors to measure the temperature of the superficial temporal artery under the skin of the forehead. There are both contact and non-contact models available. They are suitable for all ages, noninvasive, provide fast readings in a matter of seconds, and can be quickly reset for multiple readings. The Pangao Advanced thermometer offers the added feature of rapidly switching from forehead to ear mode. Purchasing a professional, hospital-grade device will give confidence in quality and accuracy.

The accuracy of your reading is reliant upon the correct use of your forehead thermometer. Sweat, hair and even make-up on the forehead can compromise the reading. Please ensure that you read and retain the manufacturer’s instructions supplied with your device. 

Non-contact thermometers are now an essential tool for screening procedures carried out worldwide as a result of the Covid-19 pandemic as they minimise direct contact and reduce the risk of spreading disease. 

Forehead temperature readings are 0.6°C (1°F)  cooler than oral temperature readings.

Digital Thermometers

Digital thermometers are a fast, easy to use, accurate and inexpensive choice. They can be used in the mouth, rectum or armpit and usually give a reading in 1 minute or less. Rectal readings are most accurate but not always convenient. If you require a digital thermometer for fertility purposes please choose a Basal version, mentioned below. 

Please be aware that an armpit (axillary) reading will be lower than an oral reading by approximately 0.6°C (½ to 1°F), while a rectal reading will be higher than an oral reading by about 0.6°C (½ to 1°F).

Basal thermometers, also digital, work on the same principle as regular digital thermometers but have a higher degree of accuracy as they measure in smaller increments. They are most often used by women wishing to monitor their monthly cycle to conceive. They measure the basal body temperature, which is the body’s lowest temperature whilst resting. Please see the resource below.

https://www.thenutritionstore.ie/digital-basal-thermometer-1303.html

Infrared Ear Thermometers (Tympanic)

Ear thermometers measure the temperature of the tympanic membrane or eardrum using infrared sensors. They are extremely fast, easy to use and accurate. They are especially useful with small children as they are least invasive and give a reading almost instantly. However, infants and babies have such tiny ear canals that it is necessary to wait until your baby is at least 6 months old before using an ear thermometer. They are otherwise suitable for all ages. 

Tympanic temperature is higher than oral temperature by 0.3°C - 0.6°C (0.5°F - 1°F).

Tympanic thermometers are not a one size fits all device as no two ears are the same shape and size and they may not be suitable for particularly small ears. A build-up of earwax may cause an obstruction and result in an inaccurate reading. Protective plastic caps will need to be replaced after every use.

The Nutrition Store is a preferred supplier of thermometers to the Health Service Executive (HSE) in Ireland and its range of approved medical thermometers can be viewed here

https://www.thenutritionstore.ie/healthcare/thermometers.html