Mercury-in-glass thermometers have largely been phased out of home use due to the toxicity of the liquid element they contain. Modern thermometry relies on safer and often more accurate technologies, providing consumers a variety of choices to measure body temperature at home. These mercury-free devices, which include digital contact probes and rapid infrared scanners, have made obtaining a temperature reading faster and easier. Understanding how to correctly use and interpret the readings from these newer thermometers is essential for accurate health monitoring.
Interpreting Digital Displays
Standard digital thermometers use an electronic sensor, typically a thermistor, within a probe tip to measure temperature by monitoring changes in electrical resistance. These probe-style devices can be used for oral, axillary (armpit), or rectal measurements, and they require a stabilization period to capture the final reading. To begin, ensure the device is clean and turn it on; the display usually shows the last measurement or a standby symbol like “Lo.”
The probe must be held securely in the measurement location until the device signals completion, usually with a series of audible beeps. This stabilization time allows the sensor to equilibrate fully with the body temperature, often taking between 10 and 60 seconds depending on the model. Wait for this signal rather than removing the probe as soon as the number on the liquid crystal display (LCD) begins to climb. The final, stable temperature is then clearly displayed on the LCD screen, which is the value you record.
Using Infrared and Temporal Scanners
Infrared thermometers, including temporal artery and tympanic (ear) models, measure thermal radiation emitted by the body, providing a nearly instantaneous reading without requiring a long wait time. Temporal artery thermometers are held close to the forehead. Some models require a gentle swipe across the forehead while scanning the temporal artery to capture the highest temperature. Other non-contact infrared thermometers are held a specific distance away, often about one inch from the center of the forehead.
For the most accurate result, the target area must be clear of hair, sweat, or cosmetics, which can interfere with the infrared signal. Once the measurement is complete, the final temperature digit appears on the screen, often accompanied by a single beep or a color-coded backlight. Tympanic thermometers work similarly by measuring infrared heat from the eardrum, requiring the probe to be correctly positioned within the ear canal for an accurate assessment.
Temperature Scales and Site Interpretation
Once a number is displayed, the first step is to note the temperature scale, which will be indicated by a small degree symbol followed by either a ‘C’ for Celsius or an ‘F’ for Fahrenheit. Most modern digital devices allow for an easy switch between these two scales by holding down a specific button. If a conversion is necessary, the formula to change Celsius to Fahrenheit is \(F = C \times 1.8 + 32\).
Consider where the temperature was taken, as readings vary significantly by site. A rectal temperature is considered closest to the body’s core temperature, reading \(0.5^{\circ}F\) to \(1.0^{\circ}F\) higher than an oral temperature. Conversely, readings taken from the axillary or temporal artery sites are \(0.5^{\circ}F\) to \(1.0^{\circ}F\) lower than a comparable oral reading. Understanding these differences helps determine if a measured value suggests a significant elevation.