For years we've been told (and learned in school) that 98.6 degrees Fahrenheit is the normal body temperature of humans. But... it turns out it's not. It's actually a bit lower - closer to 97.7 degrees F. It's the lowest around 6:00 in the morning - 97.5 degrees, and it is highest around 4 to 6 pm - 98.5 degrees F. Women tend to be about 0.2 degrees warmer than men. These were the findings of a crowdsourced smartphone study (with 329 people participating) by researchers at Boston Children's Hospital.
It turns out that other research has also said this for 2 decades. Huh? And yet the outdated 98.6 degree temperature persists in our culture. From Scientific American:
Normal Body Temperature Is Surprisingly Less Than 98.6
Normal body temperature is 98.6 degrees Fahrenheit, right? Not so. There is no baseline for humans, and even if there was, it would be closer to 97.7 °F. Temperature also varies across the day, peaking in late afternoon and bottoming out in early morning. It is slightly higher for women than for men as well. For two decades research has debunked the benchmark, set way back in 1868, yet it persists. One important ramification, says Jonathan S. Hausmann, a rheumatologist at Boston Children's Hospital, who led the latest study, is to redefine fever. Most doctors use 100.4 °F or higher, but if “normal” is lower, then the fever threshold should be, too. It also should vary with the daily pattern and be tailored to each individual, Hausmann says: “A child at 99.0 °F at 4 A.M. may be highly abnormal but at 4 P.M. could be within normal limits.”