Human body temperature cooler than we thought, new study shows

Researchers from Julie Parsonnet's team at Stanford University in California analyzed hundreds of thousands of body temperature measurements over the past 150 years. The conclusions are clear: humans' average body temperature is systematically decreasing. Although a new precise standard has not yet been established, scientists agree: In fact, what’s normal depends on the person and the situation, and it’s rarely as high as 98.6 F," summarizes Julie Parsonnet.

The research included 677,000 temperature measurements from different periods, encompassing data on Civil War veterans, people born in the first half of the 19th century, measurements from the 1970s, and data from 2007-2017 collected from Stanford Health Care patients.

The collected data clearly indicate a systematic decrease in the average human body temperature, roughly about 0.05 degrees Fahrenheit per decade. One possible reason for this phenomenon is that German physician Carl Reinhold August Wunderlich established the body temperature standard from 97.9 to 98.6 degrees Fahrenheit in the mid-19th century. At that time, the health condition of an average person could have been worse than today due to frequent inflammations, which could have raised the average body temperature.

Scientists emphasize that many factors affect the results of body temperature measurements. These factors include the location of measurement (mouth, armpit, rectum), time of day, gender (women’s temperature is slightly higher and changes depending on the menstrual cycle), as well as metabolism, the composition of the last meal, and the time that has elapsed since then. The quality of measurement instruments is also important.

For this reason, researchers have not indicated a new, specific standard for body temperature, only noting that it is currently lower than commonly accepted. As Julie Parsonnet notes, modern people's physiology differs from that of people in the past.