One woman's viral fever question sparked a very real debate. Is 98.6 outdated?

Yahoo

26-02-2025

Perhaps our body temperature isn't 98.6 degrees Fahrenheit — or at least not anymore.
One woman, while laying down while feeling sick, posited that on TikTok. Citing research that the more common average body temperature of today is actually 97.9, she mused: "Should we adjust our idealization of when a fever actually happens? I have a normal body temperature of 97.6, but I feel horrible but my temperature is only 99.1."
Her late January video quickly racked up more than 400,000 views and 1,600 comments, with many users sharing their temperature also tends to skew lower than 98.6.
So why do we think of 98.6 degrees as healthy, and when are we actually sick?
The answer is critical, especially amid winter respiratory illness season, as the flu, COVID-19 and common colds circulate.
The number of 98.6 degrees was based on millions of temperature readings of 25,000 people in the mid-19th century by a German physician, according to Dr. Julie Parsonnet, the George DeForest Professor of Medicine and an epidemiologist at Stanford Medicine. In Leipzig, Dr. Carl Reinhold August Wunderlich wrote down what he thought was normal, then looked at differences between men and women, age and time of day of people.
The research, while not flawed, was based on people's lives about 170 years ago, said Parsonnet, who authored a study on body temperatures since the Wunderlich study.
'We are not the same people that we were in the middle of the 19th century,' she told USA TODAY.
When Wunderlich studied temperatures, life expectancy was in the late 30s, about half as long as Americans live today, Parsonnet said. People didn't have access to regular health care, antibiotics or adequate living standards. Illness and death from tuberculosis, pneumonia, dysentery and syphilis, among other illnesses, were common, Parsonnet said.
Altogether, people dealt with constant inflammation, putting our immune systems in overdrive to fend off pathogens, which raised our body temperature.
In her study, Parsonnet analyzed over 677,000 body temperatures, measured orally, from three different cohort populations in the U.S. spanning nearly 160 years. Researchers found body temperature has decreased over time. Dozens of other studies have found lower temperatures since then.
In a follow-up study, Parsonnet and researchers found average body temperatures, ranged from 97.2 degrees to 98.4 degrees. The 'normal' temperature, they found, is closer to 97.9 degrees. A 2017 study, using records of more than 35,000 patients, also found average temperature at nearly 97.9 degrees.
Women have higher temperatures than men, and older people are usually colder. Other factors determine body temperature, such as time of day (cooler earlier in day) height (the taller, the colder as heat spreads) and weight (heavier is warmer).
Parsonnet developed a personalized calculator to determine our normal body temperature by sex, age, weight, height and time of day.
Given our range of temperatures, it's hard to say when someone is sick if you're solely going by body temperature. Typically, a temperature above 100 degrees is considered a fever, but this may not be the case for everyone.
'Knowing who you are is important,' Dr. Heidi Zapata, an infectious disease specialist at Yale School of Medicine who studies the immune system, told USA TODAY. 'If you think something's off, you should further investigate. Go see (a doctor), and see what's going on.'
Someone can be really sick and not have a high temperature, Zapata added. For example, older people often don't mount high temperatures even when they're ill. But having a fever is usually a telltale sign that someone has an infection.
After all, Wunderlich wrote in 1871: "A normal temperature does not necessarily indicate health, but all those whose temperature either exceeds or falls short of the normal range, are unhealthy."
People should check a range of their symptoms, especially as flu has reached record levels of hospitalizations.
Importantly, if someone is feeling sick, try to stay at home, according to the Centers for Disease Control and Prevention. People should stay up to date with vaccines, practice good hygiene, improve indoor air quality and get treatment to reduce risk of severe complications. If people have to leave their home, they should test to check for illness, wear a mask (such as an N95) and socially distance.
This article originally appeared on USA TODAY: Is average body temperature 98.6? Here's what to know