Forehead thermometers may be less accurate than other thermometers, such as oral or ear thermometers. Wearing headwear beforehand or having sweat on the forehead could affect the reading.

Forehead thermometers provide a quick and sterile way to assess an individual’s temperature. They use infrared sensors to measure temperature. They may be easier to use than other thermometers with children and when assessing large groups of people quickly.

This article examines the accuracy of forehead thermometers compared with other types of thermometers. It also looks at how forehead thermometers work, how to use them, and the best way to take a person’s temperature.

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For general use at home, forehead thermometers will give an idea of whether or not an individual has a fever.

However, according to a 2020 study, forehead thermometers are less accurate than other methods of reading temperature, such as oral, rectal, or tympanic (ear) temperature readings.

The environment in which a person uses a forehead thermometer can also affect its accuracy, according to the Food and Drug Administration (FDA).

The FDA writes that a draft, direct sunlight, or a radiant heat source could affect the temperature reading and make it inaccurate.

The reading could also be inaccurate if a person has been wearing a head wrap or headband before taking it or if they have sweat or dirt on their forehead.

A 2013 study comparing forehead and ear thermometers found that both devices returned lower readings than rectal thermometers.

The authors discovered that the difference between the two types of thermometers was particularly notable for forehead thermometers. They concluded that forehead thermometers are not ideal for use in a hospital setting and pediatric practice.

Forehead thermometers use infrared sensors to pick up on infrared radiation that the body produces. Although infrared radiation is not visible, a person may be able to feel it as heat.

A person can take someone’s temperature with a forehead thermometer by holding the thermometer a few centimeters away from the center of their forehead, just above the eyebrows. The exact positioning will depend on the manufacturer’s instructions.

A lens inside the thermometer focuses infrared radiation that the person emits onto a thermopile, which is a small electronic device that converts the infrared radiation into heat and then again into electricity.

The thermometer measures this electrical reading and displays the result on the screen of the thermometer.

In the United States, thermometers will usually display the temperature in °F. In many other countries, thermometers will display the temperature in °C.

It will only take a person a few seconds to take a temperature reading with a forehead thermometer.

Studies using children have investigated the accuracy of different types of thermometers.

One comparison study of rectal, ear, and forehead thermometers in a hospital setting found that ear thermometers were much more likely to detect fever than forehead thermometers. A rectal temperature reading confirmed cases of fever, and the authors recommended rectal temperature readings for exact measurements of temperature.

Another study found that the difference between ear thermometer measurements and forehead thermometer measurements ranged from 2.1–2.2°C (3.78–3.96°F) across two experiments.

The authors of this 2020 study concluded that using a forehead thermometer to screen large groups of people for fever quickly is acceptable. However, they also wrote that forehead thermometers might not be the most suitable way to determine accurate body temperature measurements when compared with ear thermometers.

The general advice is to avoid using a glass thermometer. According to the National Capital Poison Center, glass thermometers can cause injury if the glass breaks. Additionally, some glass thermometers contain liquid mercury, which is toxic to humans.

If a person comes into contact with mercury from a thermometer, they should seek medical attention immediately. They should also get advice from a poison control center so they can safely clean up the spillage.

For an infant or small child, the most accurate way to obtain an accurate temperature is with a rectal thermometer.

To do this, a person should place petroleum jelly on the bulb of a rectal thermometer. Then they should lay the infant or child on their back, with their legs in the air. Children can also lie face-down.

The person should then spread the infant or child’s buttocks and insert the bulb of the thermometer 0.5–1 inch into the rectum.

The person should remove the thermometer after 3 minutes or when the thermometer beeps to finish the reading.

For adults, or children who can hold a thermometer in their mouth, oral temperatures are the most accurate.

To measure temperature orally, a person should insert the probe end of the thermometer underneath the tongue and close the mouth. The person can use their lips to hold the thermometer in place.

They should then leave the thermometer in place for 3 minutes or until it beeps.

According to the FDA, there are a few steps to take prior to using a forehead thermometer:

  • reading the manufacturer’s instructions
  • being aware that environmental factors can alter the reading (including drafts, direct sunlight, and temperatures below 60°F or higher than 104°F)
  • placing the thermometer in the testing environment for 10–30 minutes prior to testing so it can adjust
  • ensuring the testing area of the forehead is clean, dry, and easily accessible

To use the forehead thermometer, a person should hold the sensing area perpendicular to the forehead at the distance that the manufacturer recommends.

A person should then hold the thermometer steady and ask the subject to stay still to take their temperature.

Some models will have lights to guide the person on where to aim the sensor. A person should then press a button to start the reading and wait until the device beeps or flashes the temperature reading on a screen. This should only take a few seconds.

A person should not touch the sensor and must keep it clean and dry.

Forehead thermometers have become a popular option to scan large numbers of people, especially during the COVID-19 pandemic.

Forehead thermometers can quickly return a temperature result and do not require any contact between people. They have good levels of accuracy, and a person can use a forehead thermometer at home.

However, other forms of temperature readings, including oral, rectal, and ear readings, may provide greater accuracy and be more suitable for use in hospital settings.

To ensure they get the most accurate reading, a person should read the manufacturer’s instructions and make sure the forehead is clean and free of hair or headwear in the measurement area.