Observing a temperature difference between the left and right ears when using an ear thermometer is common. This variation usually reflects the thermometer’s sensitivity to small physical and environmental factors, rather than a serious health problem. Understanding the science behind this measurement, along with the common and anatomical factors at play, allows for a more accurate interpretation of the results. This clarifies why one ear might consistently or temporarily register a higher temperature than the other.
How Ear Thermometers Measure Temperature
An ear thermometer estimates the body’s core temperature by measuring the infrared energy radiated from the eardrum (tympanic membrane) and surrounding tissues. The eardrum is the preferred site because it shares a blood supply network with the hypothalamus, the brain region regulating core body temperature. This shared arterial connection, primarily originating from the carotid artery, means the eardrum’s temperature closely mirrors the body’s control center.
The measurement is only accurate if the probe is aimed directly at the eardrum. Obstruction or misdirection of the infrared sensor causes it to read the cooler temperature of the ear canal wall instead of the vascular eardrum. This reliance on a clear line of sight to a precise, warm location makes the reading highly susceptible to variations in technique and ear canal conditions.
Common Causes of Inconsistent Readings
Temperature differences between the two ears frequently relate to user technique and temporary physical obstructions. Improper angle or depth when inserting the probe often causes error, as the sensor fails to fully capture the infrared heat from the eardrum. For adults, the ear canal must be straightened by gently pulling the outer ear up and back to align the probe with the eardrum.
The presence of ear wax (cerumen) is another common factor, as it can act as an insulating barrier or physically block the thermometer’s view. Cerumen buildup tends to lower the temperature reading, sometimes by approximately \(0.24^{\circ}F\). External factors also influence readings; sleeping on one side can temporarily elevate that ear’s temperature due to localized heat retention and increased blood flow. Conversely, exposure to cold air or recent use of cold ear drops can suppress a reading, making it appear lower than the other ear.
Anatomical and Physiological Influences
Inherent biological differences between the left and right sides of the head can contribute to consistent minor temperature asymmetry. The ear canal varies in size, shape, and curvature from one ear to the other. This variation affects how deeply the probe can be inserted and how well it seals the canal from cooler ambient air. A wider or more curved ear canal can hinder the probe’s ability to focus on the eardrum, leading to a consistently lower reading in that ear.
Physiological asymmetry in the vascular supply may also play a role, despite the shared carotid artery origin. The precise distribution of blood vessels and venous drainage patterns surrounding the eardrum are not perfectly mirrored. These minor variations in blood flow can cause one side to retain or dissipate heat marginally differently than the other. This results in a small, non-concerning temperature difference, often less than \(0.5^{\circ}F\), even in healthy individuals.
When to Trust the Reading and When to Seek Advice
When faced with two different ear temperatures, rely on the higher reading as the most accurate indicator of core body temperature. The lower reading is likely an artifact caused by technical or environmental factors, such as improper probe placement or ear wax interference. To confirm the temperature and minimize procedural error, take multiple readings (typically three) in the ear that provided the highest initial result.
If the difference between the ears is persistent and significant (perhaps \(1^{\circ}F\) or more) and cannot be corrected by adjusting technique, further attention may be warranted. A large, unilateral difference could indicate a localized issue, such as an ear infection, inflammation, or fluid buildup, causing the affected ear to read higher or lower. While minor asymmetry is normal, consult a medical professional if the persistent difference is substantial or if the higher reading indicates a fever accompanied by other symptoms.