In the nearly two centuries since German physician Carl Wunderlich established 98.6°F as the standard “normal” body temperature, it has been used by parents and doctors alike as the measure by which fevers — and often the severity of illness — have been assessed. Over time, however, and in more recent years, lower body temperatures have been widely reported in healthy adults. A 2017 study among 35,000 adults in the United Kingdom found average body temperature to be lower (97.9°F), and a 2019 study showed that the normal body temperature in Americans (those in Palo Alto, California, anyway) is about 97.5°F. it was clear that something about human physiology could have changed. One leading hypothesis is that we’ve experienced fewer infections over time due to improved hygiene, clean water, vaccinations and medical treatment.
— source by University of California – Santa Barbara | Oct 28, 2020