The 98.6° Temperature Myth

When you were a kid, you probably knew that to score a magical sick day home from school, you needed to have a fever. When the thermometer came out of your mouth, it had to read higher than 98.6º or you were going to school. You may be shocked to learn that the average body temperature isn’t 98.6º at all. A 2023 study found that not only is the average body temperature more like 97.9º, but an individual’s normal range can be influenced by gender, age, height, weight, and even the time of day it’s taken. The 98.6º myth originated in the 19th century with a single doctor, and despite evidence to the contrary, it has persisted ever since. In 1851, Carl Wunderlich, the director of the hospital at Leipzig University, began going from room to room with a comically large thermometer in tow. He concluded that the average human body temperature was 98.6º, and no one questioned his average for 140 years. Then, in 1992, Philip Mackowiak — a professor of medicine at the University of Maryland, decided to test Wunderlich’s average. He proposed raising the threshold for fever to 98.9º for temperatures taken in the morning and 99.9º taken at other times. The CDC puts the fever threshold at 100.4º or higher. It’s been more than three decades since Mackowiak’s study and other research that supports his findings, yet the newer data has still not taken hold among medical professionals or the public. Part of the problem may be psychological: We cling to beliefs despite evidence to the contrary — a phenomenon called "belief perseverance." It’s a significant force upholding a surprising number of medical myths. The idea humans should drink eight glasses of water a day? Not science. Sugar causes hyperactive behavior? Nope. Reading in dim light harms eyesight? Not really. Unlearning persistent myths — especially ones loaded with the weight of medical authority — is difficult at best.