Why Human Body Temperature Is Gradually Declining
Modern research suggests the traditional 37°C benchmark may no longer reflect human physiology.
1The 37°C Benchmark
In the 1860s, German physician Carl Wunderlich established 37°C as the standard human body temperature. Based on over one million measurements from 25,000 patients, this value became the universal diagnostic reference for fever. However, recent scientific studies suggest this historical benchmark may be outdated for the modern human population.
2Evidence of Cooling
Modern data indicates that human body temperature has steadily decreased over the last 150 years. Research led by Julie Parsonnet at Stanford University analyzed 190,000 measurements taken between 1862 and 2017. The findings reveal that the average temperature for American men is now approximately 0.59°C lower than historical records.
3Global Trends Observed
This cooling trend is not limited to industrialized nations. Anthropologist Adrian Jaeggi observed that the Tsimané people in the Amazon experienced a drop from 37°C to 36.5°C between the early 2000s and 2018. These rapid changes occurred alongside significant socioeconomic shifts and improved access to modern healthcare and sanitation.
4Health and Immunity
Experts suggest that lower temperatures reflect a healthier population compared to the 19th century. Chronic inflammation from conditions like tuberculosis and poor dental health previously forced immune systems to work harder, consuming more calories and generating heat. Today, better medical treatments and vaccines have significantly reduced these systemic stressors.
5Thermal Neutrality Impact
Modern environmental control plays a crucial role in regulating our internal heat. With widespread access to air conditioning and central heating, humans spend most of their lives in a thermal neutral zone. Consequently, our bodies expend less energy maintaining a stable temperature, which contributes to a lower average metabolic heat.
6Calibration Debate
Historian Philip Mackowiak argues that Wunderlich’s original measurements might have been skewed by inaccurate 19th-century glass thermometers. He noted that these instruments were often calibrated incorrectly, potentially overestimating temperatures by up to 2°C. However, other researchers maintain that the cooling trend remains visible even when accounting for instrument calibration differences.
7Rethinking Diagnostic Limits
Medical authorities are beginning to adjust their reliance on the rigid 37°C standard. Major references like Harrison's Principles of Internal Medicine have updated their guidance to reflect these findings. Experts emphasize that temperature is a dynamic variable rather than a fixed threshold, making individual context more important than a single number.
8Clinical Significance
While the average has shifted, extreme values still signal underlying health issues. Temperatures below 35°C or above 40°C remain critical indicators of serious physiological distress. Ultimately, the decline in average body temperature serves as a biological marker of how significantly human health and living conditions have evolved over time.
Original article: BBC News Brasil — Why Human Body Temperature Is Gradually Declining