Non-contact infrared thermometers (NCITs) have become a common tool for quickly assessing body temperature, offering a hygienic advantage over traditional contact methods. These devices detect the infrared energy, or thermal radiation, naturally emitted from the body’s surface. The NCIT measures the skin’s surface temperature, which internal algorithms then process to estimate the body’s internal, or core, temperature. This allows for rapid screening without physical contact, making them useful for measuring infants or screening large groups.
The Preferred Location: Temporal Artery Scanning
The most accurate location for using an NCIT to estimate core body temperature is the forehead, specifically targeting the superficial temporal artery (STA). This major blood vessel is fed by the carotid artery, which supplies the brain. Because its blood flow closely reflects the temperature of the blood originating from the heart, the STA is an ideal measurement site.
The artery is close to the skin’s surface, allowing the sensor to capture thermal radiation effectively. Many thermometers utilize a scanning motion across the forehead to ensure the sensor intersects the STA, whose location varies slightly. The device records the highest temperature detected during this sweep, focusing on consistent, deep blood flow to overcome general skin temperature variability.
Targeting the temporal region provides a stable temperature reading because the artery is not significantly affected by external cooling or heating. The consistency of the STA’s blood flow is maintained by the body’s thermoregulatory mechanisms. Correct use involves aiming the sensor across the entire temporal area, from the center of the forehead toward the hairline, to ensure the artery is fully scanned.
Technique for Accurate Non-Contact Measurement
Obtaining a valid temperature reading with an NCIT requires adherence to specific operational steps. The distance between the device and the measurement site must be precisely maintained according to manufacturer specifications. Most devices recommend a close range, typically 1 to 5 centimeters, to ensure the sensor captures the target area accurately. Moving the device too far away can include cooler ambient temperatures, resulting in an inaccurate reading.
The sensor must be held perpendicular to the skin’s surface when the measurement is taken. Positioning the device at an angle can cause the sensor to reflect thermal energy or measure an oblong area, both introducing error. Some models require a smooth, continuous scanning motion across the forehead, while others use a single-point measurement. Always follow the specific instructions for the device, as algorithms are calibrated for a particular technique.
Allowing the thermometer to stabilize in the measurement environment is critical for accuracy. If the device is brought in from a colder or warmer location, its internal components need time to acclimate, often 10 to 30 minutes. Holding the sensor steady during the process is also necessary because movement can blur the infrared image, resulting in a lower or unstable temperature value.
Why Other Body Areas Are Unreliable
Using an NCIT on other body parts, such as the neck, wrist, or cheeks, yields unreliable results for estimating core body temperature. The fundamental issue is the difference between the surface skin temperature and the internal core temperature the device estimates. Skin temperature is highly variable because it serves as the body’s primary interface for heat exchange with the outside world.
The temperature of exposed skin is easily influenced by environmental factors like drafts, air temperature, and radiant heat sources. These areas lack the deep, consistent blood flow of the temporal artery. Consequently, the NCIT measures only superficial skin temperature, which has little correlation with the temperature of the internal organs.
The algorithms within NCITs are specifically designed and validated for the thermal characteristics of the forehead skin over the temporal artery. When the device is used on a different anatomical site, the internal calculation that converts the raw infrared reading to an estimated core temperature becomes invalid. Using the device on a non-validated site provides a misleading and often lower temperature value, unsuitable for medical screening.
Variables That Affect Infrared Readings
Several external and physiological factors can significantly interfere with the accuracy of non-contact infrared temperature measurements. These variables affect the skin’s surface temperature or interfere with the sensor reading:
Skin and Obstruction
The presence of moisture on the skin, such as sweat, can rapidly cool the surface through evaporation, causing an artificially low temperature. Similarly, thick hair, head coverings, or hats that obstruct the temporal region will prevent the sensor from accurately measuring the skin’s thermal emission.
Environmental Conditions
Ambient environmental conditions play a large role in reading reliability. Extreme room temperatures or strong drafts can affect the skin’s surface temperature and the air column between the device and the person. Direct sunlight or radiant heat sources, like nearby heaters, can introduce reflected infrared energy into the sensor, leading to inaccurately high readings.
Physiological Activity
Recent physiological activity, such as intense exercise or consuming hot or cold beverages, can temporarily alter superficial blood flow and skin temperature. To ensure reliable data, it is advisable to wait approximately 15 to 30 minutes after these influencing factors have occurred. This waiting period allows the body to return to a more stabilized thermal state.