98.6 Degrees Isn’t the Average Body Temperature Anymore

Here's what parents need to know.

When you’re a kid, 98.6 is a magic number. If your temperature creeps far enough above it, your parents are more likely to believe you need a day off from school drinking fluids and watching The Price of Right. So it’s kind of jarring to hear that it wasn’t the right number all along.

What’s Changed?

In a new study in the journal eLife, researchers from the medical school at Stanford concluded that the average normal human body temperature today is actually 97.5 degrees Fahrenheit.

They’re not throwing shade on Carl Reinhold August Wunderlich, the German physician who analyzed a million temperatures from 25,000 patients in 1869 to come up with 98.6 in the first place. Instead, they argue that changes in the human body caused our average normal temperature to fall.

“Physiologically, we’re just different from what we were in the past,” lead author Julie Parsonnet said. “The environment that we’re living in has changed, including the temperature in our homes, our contact with microorganisms and the food that we have access to. All these things mean that although we think of human beings as if we’re monomorphic and have been the same for all of human evolution, we’re not the same. We’re actually changing physiologically.”

Where does the data come from?

The new figure is based on an analysis of three different historical datasets: Union Army veterans’ medical records from 1860 to 1940, the CDC-administered National Health and Nutrition Examination Survey from 1971 to 1975, and the Stanford Translational Research Integrated Database Environment from 2007 to 2017. In total, the authors of the study considered 677,423 temperature measurements for 189,338 people in coming up with the new number.

One of the doctors who peer-reviewed the study urged the medical establishment not to ignore its findings.

“Medical norms and guidelines and thresholds for interventions need to be adjusted,” Dr. Frank Rühli of the Institute of Evolutionary Medicine at the University of Zurich told the Wall Street Journal. “That is the major issue.”

What should parents do?

On the home front, not much will change for parents. The Cleveland Clinic defines a fever as a temperature over 100.4 degrees Fahrenheit, but that doesn’t mean that every kid with a fever needs medical attention. You should save the doctor calls for these situations:

  • A fever in an infant younger than three months, as it may be their only response to a serious illness
  • A fever lasting more than five days, as a pediatrician might need to figure out the underlying causes
  • A fever higher than 104
  • A fever that doesn’t come down with fever reducers
  • A fever that causes your kid to act differently: hard to wake up, not drinking enough liquids
  • A fever that has you concerned

It’s this last point that Parsonnet echoed in a reminder that fever shouldn’t be the only consideration in evaluating you or your kid’s health.

“If you’re sick, you’re sick, regardless of your temperature.”