DO we really need to put thermometers under our tongues? Couldn't we put them above our tongues if our mouths were closed?

Anyone who has ever seen a child fidgeting, desperately struggling to keep a thermometer under the tongue, has probably wondered, Why do physicians want to take our temperature in the most inconvenient place?

   

No, there is nothing intrinsically important about the temperature under the tongue or, for that matter, in your rectum. The goal is to determine the 'core temperature', the temperature of the interior of the body.

The rectum and tongue are the most accessible areas of the body that are at core temperature. Occasionally the armpit will be used, but the armpit is more exposed to the ambient air, and tends to give colder readings. Of course, drinking a hot beverage, as many schoolchildren have learned, is affective in raising one's temperature. But barring tricks, the area under the tongue, full of blood vessels, is almost as accurate as the rectal area, and a lot more pleasant place to use.

So what are the advantage of putting the thermometer under the tongue as opposed to over it? Let us count the ways: 

Accuracy. Placing the thermometer under the tongue insulates the area from outside influence, such as air and food. As Dr E Wilson Griffin III told Imponderables, 'Moving air would evaporate moisture in the mouth and on the thermometer and falsely lower the temperature. It is important to have the thermometer under the tongue rather than just banging around loose inside the mouth because a mercury thermometer responds most accurately to the temperature of liquids of solids in direct contact with it.'

Speed. The soft tissues and blood vessels of the tongue are ideal resting spots for a thermometer. Dr Frank Davidoff, Associate Executive Vice-President of the American College of Physicians, says that compared to the skin of the armpit, which is thick and nonvascular, the 'soft unprotected tisues under the tongue wrap tightly around the thermometer, improving the speed and completeness of heat transfer'

Comfort. Although you may not believe it, keeping the thermometer above the tounge would not be as comfortable. The hard thermometer, instead of being embraced by the soft tissue below the tounge, would inevitably scrape against the much harder tissues of the hard palate (the foor of your mouth). Something would have to give - and it woul't be the thermometer. 

Davidoff concedes that, in a pinch, palcing the thermometer above the tounge might not be a total disaster:

'In principle, you could get a reasonably accurate temperature reading with a thermometer above your tounge if you hadn't recently been mouth breathing or hadn't recently eaten or drunk anything, if you held the thermometer reasonably firmly between your tounge and the roof of your mouth, and if you kept it there long enough.'