Study: Average human body temp is cooler than believed
Over the past few decades, evidence has been mounting that the average human body temperature is not 98.6 degrees Fahrenheit. Instead, most people’s baseline is a little bit cooler.
The standard of 98.6 was established over 150 years ago by German Dr. Carl Wunderlich, who reportedly took over 1 million measurements from 25,000 people. Temperatures ranged from 97.2 to 99.5, and the average was 98.6. Wunderlich also established 100.4 degrees as “probably febrile,” or feverish.
However, a September study that evaluated the temperatures of more than 126,000 people between 2008 and 2017 found that the average is closer to 97.9 degrees. Other modern-day studies have reported similar numbers.
Experts who study body temperature have differing opinions about why we appear to have gotten cooler over time. Some say it could just be a measurement issue — Wunderlich might have assessed temperatures using different methods and standards than we do today. One account reports that he used a foot-long thermometer that went into a person’s armpit.
Many factors can influence a body temperature reading, the most significant being where you take it: Rectal temperatures are reliably higher than oral temperatures, which are reliably higher than readings from the skin. Body temperature is also influenced by the time of day and the weather.
Comparing historical and modern-day data gives you “a hodgepodge mixture of observations,” said Dr. Philip Mackowiak, an emeritus professor of medicine at the University of Maryland School of Medicine, who, in a 1992 paper, was one of the first researchers to scrutinize Wunderlich’s conclusions.
Other experts think humans really have gotten cooler over the past 150 years. Our temperatures may have declined because “we are so lucky to be healthier than we used to be,” said Dr. Julie Parsonnet, a professor of medicine and of epidemiology and population health at Stanford Medicine, who led the September study.
It could be that many in Wunderlich’s sample had slightly elevated temperatures from low-grade inflammation. Better treatment of infections, improved dental care and the use of medications like statins and nonsteroidal anti-inflammatory drugs may all have contributed to a decline in inflammation since the 19th century, which in turn lowered people’s average temperature, Parsonnet said.
Regardless of the reason for the shift, many experts agreed that 98.6 degrees should no longer be considered the universal human standard. But instead of shifting the average temperature down, it should be given as a range, said
Dr. Waleed Javaid, a professor of medicine at the Icahn School of Medicine at Mount Sinai.
But if we redefine “normal” human body temperature, then what is abnormal? The Centers for Disease Control and Prevention says that temperatures of 100.4 and above qualify as a fever — a roughly 2-degree increase from 98.6. But if the average human temperature is lower, it’s possible that the temperature indicating a fever could be lower too.
Parsonnet would like to see a personalized approach to fever, in which doctors compare each patient against their own baseline so that low-grade fevers aren’t missed in people who run cooler.
Mackowiak and Javaid are not concerned about low-grade fevers being missed because of the current temperature standards. Instead of changing the definition of a fever, they said the solution may be to place less of an emphasis on fever overall and to think of it as one sign among many — something many doctors already do. (This advice also applies to parents.)