Tympanic temperature is a measurement of the body’s heat taken from the ear canal, specifically from the tympanic membrane, or eardrum. It is a common way to check for fever because readings take only a few seconds, making it a preferred method for use with children.
The Science of Ear Thermometers
The eardrum shares its blood supply with the brain’s temperature-regulating center, the hypothalamus. This shared circulation, originating from the common carotid artery, means the eardrum’s temperature closely reflects the body’s core temperature. The ear canal itself does not generate significant heat, so the measurement is determined by this shared blood flow.
Ear thermometers do not need to touch the eardrum to work; they operate using an infrared sensor. This sensor detects and measures the thermal energy, or heat, radiating from the tympanic membrane. When the probe is placed in the ear, it scans for this infrared energy and converts it into a temperature reading.
How to Take a Tympanic Temperature
Always read the instructions for your thermometer model and attach a new, clean probe cover before use. Turn the device on and ensure the person’s head is held still to prevent movement. The process of positioning the probe differs slightly based on age.
For an adult, gently pull the outer ear up and back to straighten the ear canal. In infants and young children, the ear should be pulled straight back. This allows the thermometer’s probe a clearer path to the tympanic membrane rather than the ear canal wall.
With the ear held in position, insert the covered tip into the ear opening until it creates a gentle seal. Do not use force or push the probe too deeply. Press the measurement button and hold it until the device signals that the reading is complete, often with a beep, then remove it to view the temperature.
Understanding the Reading
A normal tympanic temperature is typically around 99.5°F (37.5°C). However, a normal temperature can vary from person to person and fluctuate based on factors like time of day or recent activity. For adults, a normal range can be considered between 95.7°F and 100°F.
A fever is generally defined as any temperature above the normal range for an individual. For medical purposes, a fever is often considered a tympanic temperature at or above 38.0°C (100.4°F). It is helpful to know that tympanic readings tend to be slightly higher than oral temperatures and a bit lower than rectal temperatures.
Factors Affecting Accuracy
Several factors can interfere with accuracy. Improper technique, like not straightening the ear canal correctly, can cause the probe to scan the cooler ear canal wall instead of the eardrum, resulting in a falsely low reading.
Physical obstructions can also lead to incorrect measurements. An excessive buildup of earwax (cerumen) can block the infrared sensor. An active ear infection can alter the temperature, and a small or curved ear canal can make it difficult to obtain an accurate result.
External conditions also influence the reading. Lying on one ear can artificially warm it, leading to a high temperature. Coming inside from the cold can cool the ear canal, causing a low reading. Allow the body to adjust to room temperature before taking a measurement.