A slight difference in temperature between the left and right ears is common when using a tympanic thermometer and is usually a normal phenomenon. This device measures the heat radiated by the eardrum, which serves as a proxy for the body’s internal temperature. The small variations observed result from complex physiological factors combined with the sensitive nature of the measurement technique. Understanding these differences provides a more accurate way to interpret the reading for health assessment.
Understanding Tympanic Temperature Measurement
The ear is used for temperature measurement because the tympanic membrane (eardrum) shares a blood supply with the hypothalamus, the part of the brain that regulates core body temperature. Blood reaches this area via branches of the internal carotid artery, making the eardrum an accessible site for monitoring the heat of the blood perfusing the brain’s temperature control center.
Tympanic thermometers use an infrared sensor to detect the thermal radiation emitted by the eardrum and the walls of the ear canal. This measurement reflects the heat from the underlying circulating blood, not just skin temperature. Because the eardrum is physically close to the brain’s temperature regulation system, the temperature measured here closely follows changes in the body’s core temperature.
Physiological Reasons for Temperature Variance
The most significant biological reason for temperature differences relates to the asymmetrical nature of blood flow and venous drainage in the head. The vascular system supplying and draining the brain is not perfectly mirrored on the left and right sides. Since heat is transported by the blood, asymmetry in flow leads to subtle, measurable temperature differences.
For example, the venous drainage of the brain often shows a distinct asymmetry, with the superior sagittal sinus frequently draining predominantly into the right transverse sinus. This difference means the flow of blood, and the heat it carries, is not always equal between the two sides. This circulatory asymmetry can cause one eardrum to be slightly warmer or cooler than the other.
External and Procedural Factors Affecting Readings
Beyond internal biology, several external factors can introduce variance between the two ear temperature readings. The presence of cerumen, or earwax, can obstruct the infrared sensor’s path to the eardrum. This obstruction leads to an artificially lower reading because the wax either insulates the eardrum or blocks the emitted thermal radiation from reaching the probe.
Improper technique is a major cause of asymmetrical results. The thermometer probe must be aimed directly at the eardrum, which requires straightening the ear canal by gently pulling the earlobe. If the probe is angled toward the cooler ear canal wall instead of the eardrum, the reading will be inaccurate and lower than the true core temperature. Environmental factors also play a role, such as lying on one side just before measurement, which can trap heat and artificially raise the temperature of the covered ear.
Interpreting Temperature Differences for Health Assessment
Minor differences between ear temperatures, typically less than 0.5°C (0.9°F), are frequently observed and are not a cause for concern. Studies show that the difference between the two ears can occasionally be as large as 0.8°C in healthy individuals. For the most accurate reflection of core body temperature, it is recommended to measure both ears.
The higher of the two readings should be considered the more reliable estimate because external and procedural factors are more likely to depress the reading than to elevate it. A significant difference, such as a consistent variation of more than 1°C (1.8°F), could indicate a localized issue like an ear infection, inflammation, or a substantial blockage, warranting consultation with a healthcare provider.