Getting two different numbers from the left and right ear is common. Usually it’s the ear and the conditions of the reading that differ, not the body’s temperature. An ear thermometer reads the heat of a small spot deep in the ear, so anything that warms, cools or blocks that spot shifts the number. The practical fix is less about finding the “right” ear and more about measuring the same way, in the same ear, every time.1BIPM. Best Practice Guide: Use of Infrared Ear Thermometers to Perform Traceable Non-Contact Measurements of Human Body Temperature
How Big a Difference Between Ears Is Normal
An ear thermometer reads the infrared heat given off by the eardrum, the thin membrane at the end of the ear canal. The two eardrums aren’t identical heat sources, but they’re close. On average, the left and right ear of the same person differ by only about 0.06°C.2PubMed Central. Studying the Accuracy and Function of Different Thermometry Techniques for Measuring Body Temperature A difference under 0.2°C is generally considered too small to matter for health decisions.3PubMed Central. Studying the Accuracy and Function of Different Thermometry Techniques for Measuring Body Temperature Children vary more. In healthy children without fever, readings taken in both ears a few minutes apart differed by as much as 0.6°C.4PubMed Central. Tympanic membrane temperature as a measure of core temperature A half-degree gap between ears in a healthy child is within what’s normally seen.
Gaps get larger and less predictable once someone has a fever. In children with fever, the two ears agreed poorly, with one ear reading up to 0.4°C higher or 0.8°C lower than the other.5PubMed Central. Tympanic membrane temperature as a measure of core temperature There was no way to predict when the gap would be big or small.6PubMed Central. Tympanic membrane temperature as a measure of core temperature Adults show a similar pattern: the two ears differed more when temperature was more than 0.4°C above or below 36.7°C.7PubMed. The patient: a novel source of error in clinical temperature measurement using infrared aural thermometry Above that point the left ear tended to read higher, and below it the left ear tended to read lower.8PubMed. The patient: a novel source of error in clinical temperature measurement using infrared aural thermometry So the gap you notice may be largest exactly when you’re checking for fever.
Because gaps can reach 0.6 to 0.8°C, a reading near 38°C could land on either side of the fever line depending on the ear. Repeating in the same ear tells you more than comparing ears, and symptoms and how the person looks matter alongside the number.
Lying on an Ear or Wearing Earbuds Warms That Side
Ear readings were noticeably higher right after someone had been lying on that ear.9PubMed. Analysis of the effect of lying on the ear on body temperature measurement using a tympanic thermometer A pillow or mattress holds warmth against the ear and canal. Body and head position may also shift blood flow to one side of the head, nudging each ear’s temperature up or down.10PubMed. Effects of body and head positions on bilateral difference in tympanic temperatures A child who wakes from sleeping on their right side may therefore read higher in the right ear.
Right after waking, the ear that was facing the ceiling was exposed to room air, so it is the better choice. Otherwise, wait several minutes after they sit up.
A pillow-warmed ear can push a normal temperature closer to the fever line, though the rest of the body isn’t actually hotter. Rechecking after the child has been sitting up for a while can help show whether the first number was inflated.
Earbuds, hats and hearing protection create a warm pocket too. It’s best not to measure in an ear that has just had an earphone in it.11PubMed. The effects of earphones and music on the temperature measured by infrared tympanic thermmeter: preliminary results Gear covering the ear, such as headgear or protective wear, warms the air around the ear because heat can’t escape.12PubMed Central. Evaluation of a Wearable Non-Invasive Thermometer for Monitoring Ear Canal Temperature during Physically Demanding (Outdoor) Work Wind does the opposite, cooling the ear and producing readings that are too low.13PubMed Central. Evaluation of a Wearable Non-Invasive Thermometer for Monitoring Ear Canal Temperature during Physically Demanding (Outdoor) Work A child arriving from a windy walk may read falsely low, so let them sit indoors uncovered first. A low reading after outdoor time shouldn’t be taken as reassurance that there’s no fever.
Remove earbuds, hats or earmuffs and let the ear settle in normal room air before measuring. If you can’t wait, use the other ear and note which one you used.
Earwax Can Pull a Reading Down
Earwax sits between the thermometer and the eardrum, and it tended to lower ear readings by about 0.13°C on average.14PubMed. Effect of cerumen on infrared ear temperature measurement In some people the drop was 0.3°C or more, and in 6 of 14 people the reading was that much lower.15PubMed. Effect of cerumen on infrared ear temperature measurement When wax fully blocking the canal was removed, readings rose by about 0.2°C.16PubMed. Limitations of infrared ear temperature measurement in clinical practice Wax isn’t rare either: visible wax was found in about 3 in 10 hospital patients examined.17PubMed. Limitations of infrared ear temperature measurement in clinical practice
The thermometer is trying to see infrared heat from the eardrum, and wax in the way acts as a cooler, partly blocking layer between the sensor and that heat. The more of the canal the wax fills, the less of the eardrum the sensor can see, and the more the number is pulled down. A small amount pushed to the side of the canal may do very little, which is why the average effect is small. Because wax varies in amount and position, it can create a gap between a person’s ears that changes if the wax shifts.
Since wax lowers readings, it won’t explain an ear reading unusually high. If you suspect wax, use the ear that seems clearer and stick with it. Don’t dig with cotton swabs before measuring, since that can pack wax deeper. If one ear consistently reads lower and hearing on that side is muffled, ask a doctor about wax removal.
How You Aim the Thermometer Changes the Number
Readings taken while gently pulling the outer ear to straighten the canal differed from those taken without it, by about 0.31°C on average.18PubMed. Effect of Auricular Position on Body Temperature Measurement with Tympanic Thermometers: A Quasi Experimental Study The canal curves, and its walls are cooler than the eardrum, so a probe pointed at the wall reads low. Pulling the ear gently straightens the path so the sensor can see the eardrum. If you pull one ear correctly and not the other, you’ve created a gap that isn’t real. Which hand you hold the thermometer in or which ear you choose didn’t cause meaningful differences when technique was good.19PubMed. A comparison of temperature measurements using three ear thermometers
Good technique goes like this. For adults and older children, gently pull the outer ear up and back. For babies under about one year, pull the ear straight back. Insert the probe snugly so it seals the canal, pointing toward the eardrum. Use a clean probe cover each time and follow the device’s instructions. Reaching across a child’s head often changes the angle and how firmly the ear is pulled, so use the same posture and hand grip for each reading.
Don’t take one quick reading in each ear and report the higher one, since each may have been aimed differently. Repeat two or three times in one ear and use the consistent value.
When a Difference Points to an Ear Problem
A changed or inflamed ear can run warmer. People who’d had a type of ear surgery that removes part of the canal wall read about 0.66°C higher in the operated ear than the healthy one.20SpringerLink / European Archives of Oto-Rhino-Laryngology. Effect of the status after ear surgery and ear pathology on the results of infrared tympanic thermometry Inflammation brings extra blood flow, which warms tissue locally. An infected canal or eardrum can be warmer, and the thermometer reads that local heat, so the ear may read higher than the rest of the body and the number is a less reliable measure of the whole body. Blood flow to each side of the head and to the eardrum can also shift with nerve signals, nudging one side’s reading.21PubMed. Effects of body and head positions on bilateral difference in tympanic temperatures Healthy people show these shifts too.22PubMed. Temperament, tympanum, and temperature: four provisional studies of the biobehavioral correlates of tympanic membrane temperature asymmetries
Many causes of ear-to-ear gaps are harmless, such as lying on one side, so ear symptoms are what turn a gap into a concern. A doctor looks into the ear with a lighted scope to judge infection, which a thermometer can’t do.
Pay attention to ear pain, tugging at the ear, discharge, or muffled hearing on the warmer side, or to a gap that stays large across repeated, careful readings. Fever with ear symptoms in a young child warrants a doctor visit.
When you go, bring both readings and which ear gave each. Mention whether the person had been lying on that ear or wearing earbuds, and any history of ear surgery or tubes.
Which Ear Reading to Trust
Because each ear can read differently, the standard advice is to always measure in the same ear when tracking temperature.23BIPM. Best Practice Guide: Use of Infrared Ear Thermometers to Perform Traceable Non-Contact Measurements of Human Body Temperature Doctors monitoring children are advised to stick to one ear for the whole illness.24PubMed Central. Tympanic membrane temperature as a measure of core temperature The trend in one ear over hours tells you more than a single gap between two ears.25Public Health Reports. The Use of Infrared Ear Thermometers in Pediatric and Family Practice Offices
To choose your measuring ear, pick the one without wax, pain, recent earbud use or past surgery. Note it down so other caregivers use the same one. If that ear becomes unusable, switch and write down that you switched.
Then keep a record. Write down the time, the ear and the number each time you measure, so you can see whether the temperature is climbing, steady or falling.
If readings jump around or a fever decision depends on a few tenths, check another way. A mouth reading for older children and adults, or a rectal reading for infants, gives a second opinion. Exercise or heat can also shift ear readings, so measure after resting.
Sometimes the number matters less than the person. Babies under three months with any fever need prompt medical advice. Trouble breathing, a stiff neck, unusual drowsiness or a rash need care regardless of which ear reads higher. A fever lasting several days deserves a doctor’s view.