Infrared forehead thermometers are non-contact devices designed to offer a quick and sanitary way to screen body temperature. They are common in clinical and home settings because they provide a reading without physical contact, making them simple to use on sleeping children or large groups of people. The devices measure the heat energy naturally emitted from the skin and convert that measurement into a displayable temperature reading. Understanding their proper operation is necessary for reliable results.
The Science Behind the Measurement
The core principle involves the detection of infrared radiation, which all objects, including the human body, emit as thermal energy. The thermometer contains an infrared sensor that captures this energy given off by the skin’s surface, particularly over the temporal artery in the forehead. The temporal artery is an accessible blood vessel that runs across the forehead and provides a blood flow that reflects the body’s internal, or core, temperature.
The device then uses an internal algorithm to translate the detected skin temperature into an estimated oral-equivalent body temperature reading. This adjustment is necessary because skin temperature is lower than core body temperature. The thermometer may also factor in the ambient temperature of the room to refine the final displayed measurement.
Step-by-Step Guide to Taking a Temperature
Before beginning, ensure the thermometer has acclimatized to the room temperature for at least 10 minutes, as a sudden change in environment can affect the sensor. Check the device’s screen to confirm it is set to “Body” or “Forehead” mode, rather than “Surface” or “Object” mode. Ensure the small sensor lens is clean and free of dust or fingerprints, which can interfere with the infrared detection.
Position the thermometer probe directly toward the center of the forehead, holding it perpendicular to the skin. The ideal distance is typically between one and two inches (2–5 cm) from the skin, but always consult the manufacturer’s instructions for the specific model. Press the measurement button, keeping the device steady until you hear a beep or see the reading appear on the display.
Some thermometers may require a gentle, continuous slide from the center of the forehead to the hairline near the temple. This technique captures the highest temperature detected during the scan. Once the reading is complete, compare the displayed number to normal temperature ranges, remembering that a forehead reading may be slightly lower than an oral or rectal temperature.
Factors Influencing Accuracy
Environmental and physiological factors can lead to inaccurate readings. The presence of sweat, dirt, makeup, or oil on the forehead can cause the sensor to read a lower temperature due to evaporative cooling or interference with the infrared signal. Wearing a hat, headband, or having hair covering the measurement area can also skew the result, so the forehead should be clear for at least ten minutes before a reading.
Environmental conditions in the room play a significant role, as strong drafts, direct sunlight, or air conditioning vents can rapidly cool the skin surface. If the individual has recently entered from a cold or hot outdoors environment, the skin temperature will not accurately reflect the core body temperature. Waiting ten to twenty minutes indoors helps the body acclimatize. The physical distance between the thermometer and the forehead is also precise; holding it too far away can result in an artificially low measurement.