If the first number that pops into your head when you think about body temperature is 98.6°F, you have a study from 1851 to thank for that. Carl Reinhold August Wunderlich, a German doctor, took multiple axillary (armpit) temperatures from about 25,000 people, and based on an analysis, he established 98.6°F (or 37°Celsius) as the norm. The reality though is that normal body temperature is on a spectrum, not an absolute. Body temperature can depend on your age, the time of day, and what you were doing before you popped the thermometer in your mouth or zapped your forehead. If you’re won...