A Moment of Science

Ninety-eight Point Six–Magic Number or Medical Myth?

Hard exercise can raise your body temperature as much as four or five degrees.

Close up of thermometer

Photo: lopolis (flickr)

98.6 degrees isn't necessarily what your body temperature should be

Most home health books tell us the average or normal body temperature is ninety-eight point six degrees. Glass thermometers designed for measuring body temperature often include a marker at ninety-eight point six indicating where the mercury is supposed to stop. But what does it mean if we’re above or below that mark?

In fact, the temperature of a healthy body is so variable that there is no single normal temperature, even for an individual. For example, some parts of the body are warmer than others, so a temperature taken rectally may be a degree higher than a temperature taken orally, which is usually a degree higher than a temperature taken under the armpit.

Exercise can raise the temperature as much as four or five degrees; so if you’re running hard to make that doctor’s appointment, don’t be surprised if your temperature reads a little high. When you stop running, your temperature drops, but other factors are harder to control. During the second half of the menstrual cycle, women’s body temperatures go up about one degree. Everyone’s temperatures, regardless of physical activity, goes up and down around two degrees with the low around 4 A.M and the high around 4 P.M.

In short, everyone’s body temperature has a very wide range, probably between ninety-seven and a hundred degrees, with some even higher or lower. So does body temperature tell us anything at all? Yes, because a very high temperature, say over a hundred degrees, usually means that someone is sick. But there’s nothing magical about ninety-eight point six that makes it any different from a lot of other nearby numbers.

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