Ear thermometers, also known as tympanic thermometers, are popular for measuring body temperature due to their speed and non-invasive nature. These devices are especially appealing when taking a temperature on a restless child. The reliability of the reading depends heavily on understanding how the device works and using the proper technique.
The Science Behind Ear Temperature Measurement
The tympanic thermometer uses an infrared sensor to detect the heat energy radiating from the eardrum and surrounding tissues. This sensor collects the infrared energy and converts it into a temperature value. The eardrum is an ideal measurement site because it shares a blood supply with the hypothalamus, which acts as the body’s central thermostat and regulates core body temperature.
This common blood flow allows the temperature of the eardrum to rapidly reflect changes in the core body temperature, often faster than other common measurement sites. If the probe is not aimed directly at the eardrum, the reading will instead capture the cooler temperature of the ear canal walls, which does not accurately represent the body’s internal state.
Maximizing Accuracy Through Proper Technique
Achieving a reliable reading requires correct user technique to ensure the infrared sensor has a clear view of the eardrum. Straightening the ear canal aligns the probe with the eardrum. For adults, this is accomplished by gently pulling the outer edge of the ear up and back.
For young children, whose ear canals follow a different anatomical curve, the ear should be pulled gently straight back or down and back. A clean, disposable probe cover must be placed on the tip before insertion, as the device is calibrated to work with the cover in place. The probe should be inserted firmly into the ear canal, creating a seal to avoid interference from ambient air.
Once the thermometer signals the reading is complete, remove it. Taking multiple measurements in the same ear and recording the highest result is advisable to account for slight placement variations.
Common Causes of Inaccurate Readings
Factors unrelated to user technique can skew the temperature measurement. The most frequent issue is the presence of earwax, which can obstruct the sensor’s view or create an insulating barrier that results in a falsely low reading. A dirty or damaged probe window can similarly interfere with the collection of infrared energy, leading to a diminished temperature display.
External factors can also influence the local ear temperature. Lying on one ear for an extended period can artificially warm the area. Rapid changes in ambient temperature, like moving indoors from a cold environment, can affect the reading until the ear canal stabilizes. Furthermore, an active ear infection can cause inflammation and a localized temperature increase that does not accurately reflect the body’s core temperature.
Comparing Ear Thermometers to Other Methods
The accuracy of ear thermometers is best understood in comparison to other temperature-taking methods. Rectal measurement is considered the closest representation of core body temperature. Tympanic readings often average slightly higher than oral temperatures, by 0.5°F to 1.0°F.
While the speed and comfort of the ear thermometer are benefits, its accuracy is more sensitive to placement and environmental factors than a rectal thermometer. Forehead or temporal artery thermometers, which also use infrared technology, can exhibit greater inconsistency when compared to rectal or ear readings.
Axillary (underarm) temperatures are the least reliable, as they primarily measure skin temperature and can register up to a degree lower than internal measurements. For infants younger than six months, ear thermometers are often not recommended because their ear canals are still very small and developing, which makes accurate placement difficult.