Ear, mouth, underarm or rectal – there are many ways to take your childs’ temperature. The following article presents the different methods with their advantages and disadvantages. What is the best way to measure your child’s fever?

Taking your childs’ temperature should be simple, safe, accurate and fast. You do not want to disturb your already sick child, but you need to know the correct temperature to take appropriate action.

The core body temperature differs from the skin temperature. This is the reason why body temperature is always measured in areas of the body, that are close to the inner body: Bum, ear, mouth or armpit. The time of day will make a difference in the body‘s temperature. Usually during daytime, temperature is lowest in the morning, before getting up. Throughout the day it will rise and change based on the activity level. The temperature reading can be affected by additional influences, too: For example when your child just had a bath, a cold or hot drink or when wrapped up tightly in a thick blanket.

By definition, it is a fever, if

  • Rectal temperature is at or over 99.5 – 100.4 F (depending on depth of measurement)
  • Oral temperature is at or over 99.5 F
  • Axillary or in-ear is at or over 99.5 F
  • In-ear is at or over 100.4 F

Measurement Methods

There are generally two different ways to measure body temperature:

  • Contact thermometry: A resistance sensor element is in contact with the skin and changes its resistance in accordance with the temperature. Example for contact thermometers are digital thermometers. Measurement places for contact thermometers are usually:
  1. Rectum
  2. Oral
  3. Axillary
  • Infrared thermometry or IRED (infrared radiation emission detectors). Infrared thermometers measure the thermal radiation emitted by the skin without being in contact with it. Places where IRED thermometers are used today are:
  1. Tympanic membran (most accurate)
  2. Forehead

There are also mercury thermometers which however are highly toxic. They were common in the past but shouldn´t be used anymore due to better non-toxic alternatives. All thermometers describe above give you a more or less accurate one time reading. But an even better method is using a continuous thermometer that continuously takes the temperature and thus is able to provide a whole temperature curve to indicate where the child is heading in any moment.

Tactile Temperature

Most of the time, parents realize instinctively that something isn‘t right with their child. The eyes look tired, the cheeks are flushed or the breath feels hotter than normal. A parents first reaction is to place a hand lightly on the forehead, in order to assess whether it feels too warm. The problem is, however, that the temperature you feel on your child‘s forehead is depending on the temperature of your hand. Your child feels warmer, when your hand is cooler.

A slightly better method is to feel the temperature with your lips. The abundance of nerves and thinner skin in your lips can detect a fever more reliably.

This method is still not a real measurement, of course. But it can provide you with a first indication. If your kid‘s skin does feel uncommonly warm, you should rely on a precise temperature measuring method. In the following you will see a list of thermometers that are available today along with their advantages and disadvantages:

Digital Thermometers

Digital thermometers use an electronic temperature measuring technology. The measured value shows on a LCD display. They allow quick measurements, easy readability and can be acquired at low prices. Digital thermometers are used for rectal, oral and axillary measurements. Another variation is the pacifier thermometer.


Numerous doctors recommend the rectal method to determine the exact temperature, especially if your child is a baby or a toddler. But some studies have revealed weaknesses of this method.

The rectal temperature changes slowly in relation to the core temperature. So the temperature measured in the rectum has been shown to stay elevated for a time after the core temperature has already dropped, and vice versa. Also, the measured values are affected by the depth of a measurement and by conditions affecting local blood flow.

Furthermore, there are health concerns: Cases of rectal perforation have been described. Another problem is, that it is absolutely necessary, to use orderly sterilization procedures. Else, spreading of pathogenic germs that are commonly found in the rectum, may happen.

Many parents do not want to take their kids temperature rectally. And many children, especially older ones, may refuse this method.

It is also the most cumbersome way to measure the temperature: The child has to be undressed, which is complicated at night and also quite unpleasant for the child when the fever is rising, as an increasing body temperature is accompanied by a sensation of cold and the need for some rest.


The digital thermometer placed under the tongue (sublingual) is also one of the common temperature measurement methods. Measured values were found to be about 0,3 degree below the values measured rectally.

The difficulty of this method is, that results can easily be distorted: Oral themperatue measuring relies on the mouth keeping sealed and the tongue pressed down for a few minutes. Children younger than 5 or 6 years are not able to master this, they are prone to bite on the thermometer. So this method cannot be used in younger children. Also, the child has to breath through the nose – difficult, when having a blocked nose or a cough.

For at least 10 minutes before the measuring, the child should not have consumed any foods or beverages as this might distort the measured value.

A general conclusion is, that this method delivers good results with older children. It shows, that accuracy may increase with the age of the child, which is due to the ability to use the correct technique. The preciseness of the oral measurement lies between that of under arm and rectal measuring. Most older children accept this method, as it is not much of an intervention.


On the pro side is that axillary temperature is easy to measure and most kids accept it without any difficulties. This method is the most used one by a number of parents since it is very convenient and without much of an intervention. But young children are not able to seal the axillary as it is necessary to yield a reliable result. The thermometer has to remain directly in place over the axillary artery. Newer thermometers here are patches that can be glued to the skin under the armpit to continuously monitor temperature.

However, in comparison to oral or rectal measurement it is the most inaccurate one. The measurement is quite inexact and is highly influenced by ambient conditions. Approximately 0.5° have to be added to the measured results.

Despite its low sensitivity and significance this method is still considered acceptable if done properly.

Pacifier thermometer

Pacifier thermometers are based on a good idea: Many young infants refuse to have their temperature taken, especially through interfering methods. So a pacifier with a built-in temperature sensor seems like a great solution for very young kids. But as obvious as it would appear, it does not work. The reason is, that pacifier thermometers can only measure in the anterior oral area, which often might be a few tenths of a degree colder. So the measured value is of almost no significance. In addition, there are further difficulties: The measurement duration is up to 5 minutes. But babies more often than not spit their soothers out before that time. Also, most babies prefer their usual cherished pacifier, and some babies do not accept any pacifiers at all.

Infrared Thermometers

Tympanic membrane and forehead thermometers measure emitted infrared radiation. Based on this value the actual body temperature is determined. Measurements only take a few seconds which is noticeably more comfortable for the child. Particularly in-ear thermometers are enjoying increasing popularity amongst parents.

Tympanic Membrane (In-Ear)

Ear thermometers measure heat rays (infrared rays) emitted from the tympanic membrane and surrounding tissue. Big advantage of this measurement is that tympanum is easily accessible and supplied with blood from the same vessels as the hypothalamus, the body‘s temperature controller. This ensures a very accurate temperature measurement within a few seconds.

This method does have several advantages in usability, too. As it is a very quick measurement, the child does not have to hold still for a long time and does not have to be undressed for every measuring. The ill child is hardly disturbed. It usually works well for children who refuse to have their temperature taken rectally.

But there are a few cons: A precise handling and a certain amount of practice is necessary to avoid incorrect measurements with the infrared beam of the instrument. The tympanic membrane has to be hit by the infrared beam or else results will vary very much from the real value making a correct reading very hard. The device instructions have to be observed, otherwise the measurement is inconclusive.

Several things can affect the measured temperature in the ear, for example, laying on one ear, an ear infection or in most cases an unfavorable angle of the thermometer during measurement. Also, for very young children auditory canals might be too narrow.

In-ear infrared thermometers have lot of advantages, its biggest weakness, however, lies in its unique selling point, the instant measurement: Infrared thermometers actually don´t measure but estimate a temperature according to a radiation emission curve. But in order to be able to estimate accurately measuring angle needs to be exact which is hard in every day use. Measurement errors caused by the short measuring time occur too frequently.


Maybe the most comfortable method to take the temperature is via forehead thermometer. An infrared sensor measures the temperature within a few seconds. There are different models: Simple devices, which are to be glided over the skin and more modern instruments, which perform contact-free temperature measurements. This is, of course, a very hygienic method to take the temperature. And there are further advantages: It is probably the least disturbing method, as measurements in body orifices are not necessary and it offers the highest measuring speed. Therefore, kids usually accept this method readily. It is even possible, to take the temperature, while the child is asleep.

But the decisive disadvantage is, that temporal thermometers are very imprecise. As the measurement is made on the skin, it does not reflect the core body temperature. Also, these thermometers seem to have the widest variations of measurement results compared to other methods.

What is more, temporal thermometers must be utilized correctly, incorrect use leads to erroneous and therefore meaningless results.

Continuous Temperature Measurements: degree°

A completely new approach is the degree° thermometer which continuously takes the body temperature via the infrared method at the tympanum. This way, usability & accuracy disadvantages of the instant infrared thermometers are erased still having all the advantages of in-ear thermometers. And even more, continuously taking the temperature parents get a temperature curve that is able to indicate them the state of the fever, i.e. if it´s rising, falling or at a constant level at any time. Which is a highly relevant information for making decisions about a possible treatment.  Via smartphone, parents can watch their kid‘s temperature and can set alarms, to be notifies when  temperature reaches a certain level or rises too fast. So parents are always precisely informed how their child is doing. Also at night, the child‘s temperature is well monitored. degree° is comfortable and does not disturb the child‘s sleep.

AccuracyEasy to useContinuousComfortableSuitable for Babies and Toddlers