For generations, we have been told that normal human body temperature is 37°C. But scientists have discovered something surprising. Our bodies appear to be getting
cooler. Research suggests that the average human body temperature has gradually fallen over the past 200 years, raising an interesting question. Are modern humans physically different from our ancestors?
A major study by researchers at Stanford University, published in eLife in 2020, examined more than 6.77 lakh temperature readings collected across different periods in American history. The researchers found that average body temperature had declined by around 0.03°C per birth decade. This suggests that the familiar 37°C figure may no longer represent the average temperature of a healthy adult.
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How much cooler have humans become?
The Stanford researchers compared historical medical records dating back to the American Civil War with modern measurements.
Their findings showed that men born in the 1990s had an average body temperature around 0.59°C lower than men born in the early 1800s. Women showed a decline of approximately 0.32°C compared with those born in the 1890s.
Modern research has found that the average normal oral temperature in adults can be closer to 36.6°C.
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Why is human body temperature falling?
Scientists suspect that improvements in everyday living conditions may explain part of the change.
In the 1800s, people frequently suffered from infections and long-term illnesses. These conditions caused inflammation, which could increase body temperature.
Today, antibiotics, vaccines, cleaner drinking water and improved sanitation help reduce many infections.
Modern homes and offices maintain comfortable temperatures through heating and air conditioning. Researchers believe these changes could affect how much energy our bodies spend maintaining their temperature.
Still, scientists have not established a single explanation for the decline.
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The strange discovery in Bolivia
The trend extends beyond the United States.
A 2020 study published in Science Advances involving the Tsimane people of Bolivia found that their average body temperature fell from around 37°C to 36.5°C between 2002 and 2018.
Researchers examined nearly 18,000 measurements and discovered that the decline happened much faster than in the American historical records.
The exact reason remains unclear.
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Does this mean 37°C is now a fever?
No. Human body temperature changes throughout the day and varies with age, sex, activity and the measurement method.
A reading of 37°C can still be completely normal.
Stanford researcher Julie Parsonnet said, “Physiologically, we’re just different from what we were in the past.”
The findings suggest that doctors may eventually benefit from considering each patient’s usual temperature when assessing illness.
