98.6 Isn't Our Normal Temperature Any More

Carl Reinhold August Wunderlich may not be a household name, but everyone knows the figure associated with him: 98.6 degrees Fahrenheit, which he determined in the mid-1800s to be the average human body temperature. A slew of studies has since threatened to upend Wunderlick's work, with research suggesting that number was always too high, the Wall Street Journal notes. But according to a new study in the eLife journal, it may not have been Wunderlich's number-crunching that was faulty—the human body may simply have changed over time, leading the current average down to 97.5 degrees. Stanford scientists analyzed more than 675,000 temperature readings from nearly 190,000 subjects over a span of 157 years, using everything from pension records of Civil War veterans and a CDC survey administered in the 1970s to more recent Stanford research.

What the researchers found is that, in general, temperatures of the Civil War vets were higher on average than those examined from the '70s; the latter, meanwhile, were higher than the more recent Stanford-collected temps. These figures suggest that as our environment changed over the decades, our bodies adapted. Julie Parsonnet, the lead author of the study, tells Scientific American they're not sure what the direct causes could be, but warmer clothes, better control of indoor temperatures, increasingly sedentary lifestyles, and a drop in infectious diseases could all have played a part in making us "colder." Still, the number on the thermometer may not be as important as what your body is telling you otherwise. "If you're sick, you're sick, regardless of your temperature," Parsonnet says, per the Journal. (More discoveries stories.)