We all recognize 98.6 degrees F as our normal body temperature, but that number is far from exact. In fact, it’s just an average — established in 1868 by German doctor Carl Wunderlich, who took thousands of temperature readings from participants’ armpits with a cumbersome, footlong mercury thermometer that required up to 20 minutes to register.
Multiple recent studies seek to pinpoint the norm and have raised numerous other questions along the way. Several suggest 98.6 degrees F is too high. For instance, a 1992 U.S. Army–funded report found a mean body temperature of 98.2 degrees F, while a 2018 study using smartphones to record 5,038 oral temperatures suggested 97.7 degrees F. A 2002 meta review of 20 studies reaffirmed that our temps differ when taken in the mouth, ear, armpit, or rectum. But there are some caveats to all these readings:
Your temperature fluctuates during the day, hitting a low between 3 and 5 a.m. and a peak between 4 and 6 p.m. The difference can be 1 degree F or more, depending on the individual.
Men and Women
The smartphone-based study found that men’s mean temperature was 0.18 degrees F lower than women’s. And normal body temperature decreases slightly as we age.
Wunderlich’s research 150 years ago fixed 100.4 degrees F as the flare-up of fever, a novel scientific marker for doctors to determine the onset of illnesses. The Army study determined that fever should be defined as 98.6 degrees F in the morning and 99.9 degrees F in the evening — but again taking into account bioindividuality.