Stanford scientists debunk myth: Average human body temperature cooler than 97.9°F

They assert that the previously accepted normal body temperature of 97.9 degrees Fahrenheit is stale and ineffective. This standard, which has been used for over 150 years, does not account for the significant changes our environment has undergone over time. Consequently, the body temperature of contemporary humans is cooler compared to that of their ancestors.

Scientists at Stanford University arrived at this conclusion by noticing that temperature measurements of Civil War veterans significantly diverge from contemporary data. They compared a data set of 677,000 temperature measurements spanning different time periods.

The collected data included temperature results of individuals born during the first half of the 19th century, along with readings taken in the 1970s, and measurements from patients of Stanford Health Care between 2007 and 2017. From this data, it emerged that the average body temperature of humans has been progressively decreasing, getting cooler by about 0.054 degrees each decade.

Although this drop might seem insignificant within a human lifespan, it becomes apparent over a century and a half that the standard in use is outdated.

However, the researchers decided not to specify what body temperature range should now be considered normal or abnormal. They conclude that the body temperature of contemporary humans is generally lower than 97.9 degrees Fahrenheit.

The researchers remain cautious due to the sketchy quality of historical data. The concept of monitoring body temperature as an important part of medical examination came into practice in mid-19th century. This temperature standard was established by the renowned German doctor, Carl Reinhold August Wunderlich.

However, comparing the accuracy of thermometers from the 19th century to today's devices poses a considerable challenge. Additionally, our understanding of human physiology has evolved over time. Determining whether a person considered healthy over 100 years ago would be regarded the same way today is tricky.

Sometime back, inflammation or other conditions that we now treat were either unknown or merely observed. In this day and age, we know that measuring body temperature is a more nuanced process, influenced by factors such as the time of the day, the measurement location (mouth, armpit, rectum), time passed since the last meal and even the test subject's gender. Furthermore, regular temperature changes during a woman's menstrual cycle are considered normal.

These variables started to be considered only after the earliest temperature measurement data was collected. This may have caused a slight but noticeable increase in temperature readings compared to today's records.