Are Infrared Thermometers Accurate? No

Since the beginning of Covid-19, the sales of non-contact thermometers were increased sharply.  But how accurate these devices are? When you search the question like “Are Infrared or non-contact Thermometers Accurate, you may get answer like ” Research has shown that, when used correctly, infrared or no-contact thermometers are just as accurate as oral or rectal thermometers”. Also if you ask this question to doctors, scientists, or researchers, you probably may get the same answer. However, these answers haven’t convinced me. Because myself I have tested the infrared thermometer independently and found that there is a minimum of 2 to 4° F difference between oral and non-contact thermometer.

Initially I thought that, may the non-contact thermometer I purchased was not accurate or may be it is faulty, although I purchased it from a well known brand. When I measure my body temperature using oral thermometer in various occasions, the temperature will never go below 98° F.  When my body temperature got tested using non-contact thermometers in public places like shopping malls, hospitals etc, it ranges from 94° F to 96° F. I tried to find answer for this question through internet, why infrared thermometers are showing low body temperatures than oral thermometers? I found the answer that Infrared thermometers are as accurate as oral thermometers when used correctly. When you use the infrared thermometer at a correct distance, you will get the accurate temperature measurement. This is the answer I got through internet. This answer haven’t convinced me, because practically most of the times I have observed inaccurate temperature measurements from non-contact thermometers. In order to understand how infrared thermometers works on human body, basic knowledge of physics, electronics and medical science is needed. I don’t have the knowledge of medical science, so I tried to understand working principle of infrared thermometer.

I tried to understand the working principle of a thermometer in a simpler way. What is understood is that:

Every object that has mass emits some amount of energy.  So humans too emits energy. This energy is emitted in the form of heat or infrared radiation.

Infrared thermometer measures temperature of a body by detecting the heat or infrared radiation emitted from the human body. This proves that infrared thermometer measures the body temperature emitted from the surface of the body and does not measures the inside body temperature. This outside body temperature is slightly different from inside body temperature due to environmental or other factors.

This shows that infrared or non-contact thermometers are not as accurate as oral thermometers. The temperature difference of 2° F to 4° F is not a small thing.

As we know that fever is the natural response of persons immunity to bacteria or viruses. A persons immunity raises the temperature of body from normal range while fighting with bacteria or virus.

So if a person have a fever of 102° F, he is most probably have a bacterial infection or viral infection or other unknown disease. However, if this person measures his body temperature using non-contact thermometers, sometimes it will show like 98° F to 98.7° F. Then the person may think, he do not have fever. As a result, the treatment may get delayed.

Also, some doctors or researches claimed that people will get coronavirus without any symptoms like fever. But they never mentioned which device (contact or non-contact thermometer) they used to measure fever in covid-19 patients. For example, if you measure body temperature of covid-19 patient using non-contact thermometer, it displayed 97.8 F. And if the same person body temperature is displayed 100.2 using oral thermometer, do that person has fever or not?

Conclusion: A difference of 2° F to 4° F may look like a small difference. But it shows a huge impact. A person who detected fever in oral thermometers may not detect fever in non-contact thermometers.