Infrared (IR) thermometers offer a rapid and non-contact method for measuring temperature, making them popular for use at home and in public health settings. These devices work by detecting the natural thermal, or infrared, radiation emitted by any object or person above absolute zero. The thermometer’s lens focuses this invisible energy onto a sensor, called a thermopile. This sensor converts the heat into an electrical signal that is then calculated and displayed as a temperature reading. Obtaining a measurement in just one to two seconds without physical contact makes infrared thermometry a convenient and hygienic choice.
Essential Preparation Before Measurement
Achieving an accurate temperature reading requires careful preparation of both the device and the environment. If the thermometer has been moved from a significantly different temperature zone, such as bringing it in from a cold car, it must be allowed to acclimate to the ambient room temperature for at least 15 to 30 minutes. This essential step prevents measurement errors caused by the device itself being too hot or too cold.
The sensor lens is the most sensitive part of the device and must be kept clean to ensure accuracy. Gently wipe the lens with a cotton swab moistened with isopropyl or ethyl alcohol, or a soft cloth, following the manufacturer’s specific cleaning recommendations. Never submerge the device in water or use harsh chemicals. Ensure the lens is completely dry before attempting a measurement.
Before taking a human temperature, you must confirm that the thermometer is set to the correct mode, typically labeled “Body” or “Forehead.” This mode uses an internal mathematical adjustment to compensate for the difference between cooler surface skin temperature and the warmer internal core body temperature. An “Object” or “Surface” mode measures unadjusted surface temperature. Using the object mode will typically yield a reading that is several degrees lower than an actual body temperature.
Step-by-Step Guide for Accurate Readings
The physical technique for using an infrared thermometer depends on whether it is designed for the temporal artery (forehead) or the tympanic (ear) measurement site. For a temporal artery thermometer, the area of skin being measured must be clean, dry, and clear of obstructions like hair, hats, or sweat, as moisture can cause an artificially low reading. The optimal distance for measurement is typically a short range, usually between 1 to 5 centimeters, or about three finger widths, from the skin.
Forehead thermometers often require a specific sweeping motion to accurately trace the path of the temporal artery just beneath the skin. You should gently place the sensor flat on the center of the forehead and, while holding the measurement button down, slowly glide the thermometer across the forehead toward the hairline near the ear. Some models may require you to continue the sweep to the area just behind the earlobe to capture the highest temperature, which is often the most representative.
For a tympanic, or ear, thermometer, the goal is to aim the infrared sensor directly at the eardrum, which shares a blood supply with the brain’s temperature-regulating center, the hypothalamus. To straighten the ear canal and allow a clear view of the eardrum, gently pull the outer ear. For adults and older children, pull the ear up and back; for infants or children under the age of three, the ear should be gently pulled down and back.
Insert the probe gently into the ear canal until it fits snugly, but never force it. Ensure a new, clean probe cover is used for each measurement if your model requires one. Improper alignment, excessive earwax, or recent crying can all interfere with the reading. Taking multiple readings and using the highest result increases reliability.
Understanding and Adjusting Temperature Results
The number displayed on an infrared thermometer is a surface temperature that is mathematically converted to estimate a core body temperature, meaning it will naturally differ from readings taken at other sites. Normal forehead temperatures typically range from about 97.0°F to 99.5°F (36.1°C to 37.5°C). A tympanic reading is often slightly higher, sometimes 0.5 to 1.0°F above a forehead reading. A forehead reading of 100.4°F (38.0°C) or higher is widely used as a threshold that indicates a fever and warrants further investigation.
Infrared temperature readings can fluctuate significantly due to external factors that alter skin surface temperature. Recent vigorous exercise, crying, or even lying on the side of the head can cause temporary localized warming. Drafts, cold air exposure, or perspiration will often lead to a lower, incorrect reading. If a low reading is suspected, allow the person to rest in a neutral environment for a few minutes and re-measure, or check the temperature at an alternative site.
The reported result is a function of the manufacturer’s calibration, which uses a specific algorithm to adjust the raw skin temperature to a more clinically relevant value. Some thermometers are factory-set to a fixed emissivity value for human skin, typically between 0.95 and 0.99. This calibration ensures the device provides an accurate estimate of core temperature.
Infrared readings are primarily used for screening and should be viewed in context with a person’s general symptoms and recent activity. For clinical certainty, especially in infants, a reading indicating a significant fever should be verified using a more established method, such as an oral or rectal thermometer. Always consult the specific temperature range guidelines provided in your device’s user manual, as they are calibrated to that model’s unique performance characteristics.