The average body temperature is no longer 98.6 degrees, study shows

Think 98.6 degrees is the norm when it comes to body temperature? Not quite so, according to a new study.

Stanford Medicine researchers say body temperatures range from person to person. Factors that influence body temperature include sex, age, weight and height, to name a few. It also goes up and down throughout the day, the researchers say.

“Most people, including many doctors, still think that everyone’s normal temperature is 98.6 degrees Fahrenheit. In fact what’s normal depends on the person and the situation, and it’s rarely as high as 98.6 degrees Fahrenheit,” said Julie Parsonnet, MD, a professor of medicine and of epidemiology and population health at Stanford. She authored the research that came out on Sept. 5 in JAMA Internal Medicine.

What is the current average body temperature?

Every decade since the 19th century, the average American’s body temperature has declined from 98.6 degrees Fahrenheit by 0.05 degrees Fahrenheit. That’s probably because we have better living conditions now than in the past, which reduces inflammation, and therefore body temperature. Nowadays, most people have an average body temperature closer to 97.9 degrees Fahrenheit.

So, where did the 98.6-degree figure come from? Data published in 1868 from a German doctor who collected temperatures from about 25,000 people. He reported a range of temperatures in the group saying that men and older adults had lower readings than women and young adults. Temperatures tended to run higher in the afternoons. But the average was 98.6 degrees Fahrenheit… and here we are.

In future studies, Dr. Parsonnet said she’s interested in examining personalized definitions of fever and whether having a consistently higher or lower normal temperature affects life expectancy. 

“There’s a lot of temperature data in the world, so there’s a lot of opportunity to actually learn something about it,” she said.

What temperature is classified as a fever?

It’s important to know what constitutes a medical-grade fever—that’s anything over 100.4º F, naturopathic doctor Leah Gordon, ND, tells Motherly in a separate interview. 

Anything below that temperature is not considered to be a “true” fever. It’s also good to know that not all fevers need to be treated with fever-reducing medication, especially if you or your child are still sleeping and eating relatively normally. 

The following body temperatures suggest a fever in adults:

• at least 100.4 degrees Fahrenheit is a fever
• above 103.1 degrees Fahrenheit is a high fever
• above 105.8 degrees Fahrenheit is a very high fever

The average body temperature in a newborn is about 99.5 degrees Fahrenheit. The average body temp for a child is about 97.52 degrees, and a temp above 100.4 degrees Fahrenheit is a fever. If your baby is younger than 3 months old and has a fever over 100.4º F, or if your child of any age has a fever reaching 104º F or a history of febrile seizures, call your child’s pediatrician for advice.