For the purpose of this discussion, normal core body temperature in the human body varies, but the average is 37°C or 98.6°F. Among other reasons, infections cause the body's temperature to rise. When a human's body temperature rises, it's called a fever. A fever is considered anything above 38°C or 100.4°F.
In its purist form, Fever Screening is the act of checking the internal temperature of a human being by placing an analog or digital thermometer in the mouth, armpit or rectum. This is accomplished by a qualified person with a thermometer at a check point -for instance, at an airport, factory or office building, before entry is granted. Tympanic thermometers (infrared ear thermometers) have gained popularity because they are fairly accurate, more non-contact and faster than other types. But this process takes a considerable amount of time.
Since there is a closely locked relationship between the internal and external body temperatures of humans, it has been determined that; a) to reduce screening times, and b) to reduce the risk of cross-infection between the incoming person and the screener, that thermal infrared imaging does have an acceptable level of accuracy and repeatability to be used confidently as a primary screening method.
In the primary screening process, when people with a skin surface temperature higher than that of a given set point are found, this apparent elevated body temperature warrants that person should be directed to secondary fever screening, using thermometers.
So, it can be said that thermal infrared imaging is a valid method of detecting Elevated Body Temperature in humans by using Skin Temperature Measurement -which speeds the process of entry screening for Human Febrile Temperature Screening.