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The average human body temperature is not 37 degrees – so what counts as a fever?

Over the past few decades, evidence has been mounting that the average human body temperature is not really 37 degrees Celsius. Instead, most people’s baseline is a little bit cooler.

The standard of 37 (or 98.6 degrees Farenheit ) was established over 150 years ago by the German physician Dr Carl Wunderlich, who reportedly took over a million measurements from 25,000 people. Temperatures ranged from 35.6 to 37.5, and the average was 37. Dr Wunderlich also established 38 degrees as “probably febrile”.

However, a study published in September that evaluated the temperatures of more than 126,000 people between 2008 and 2017 found that the average is closer to 36.6 degrees. Other modern-day studies have reported similar numbers.

Experts who study body temperature have differing opinions about why we appear to have become cooler over time, and whether that matters when it comes to evaluating fevers and diagnosing infections.


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Some researchers say it could just be a measurement issue – Dr Wunderlich might have assessed temperatures using different methods and standards than we do today. One account reports that he used a foot-long thermometer that went into a person’s armpit.

Many factors can influence a body temperature reading, the most significant being where you take it: Rectal temperatures are reliably higher than oral temperatures, which are reliably higher than readings taken from the skin. Body temperature is also influenced by the time of day, whether it’s hot or cold outside and even whether the person just had something to eat or drink. Readings can also vary from thermometer to thermometer, depending on how they are calibrated.

Comparing historical and modern-day data gives you “a hodgepodge mixture of observations”, said Dr Philip Mackowiak, an emeritus professor of medicine at the University of Maryland School of Medicine, who, in a 1992 paper, was one of the first researchers to scrutinise Dr Wunderlich’s conclusions. The drop in temperature may be “a true phenomenon”, he added, “but there’s no way of knowing because the data are so varied”.

Other experts think humans really have become cooler over the past 150 years. Our temperatures may have declined because “we are so lucky to be healthier than we used to be”, said Dr Julie Parsonnet, a professor of medicine and of epidemiology and population health at Stanford Medicine, who led the September study on body temperature.

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