Has the Average Human Body Temperature Changed?

For over 150 years, it’s been drilled into our minds that our “normal” body temperature is 98.6 degrees Fahrenheit. But as it turns out, this may no longer the case. A Stanford University study has found there’s a new normal. The “normal” human body temperature has dropped since 1851 when a German doctor and researcher found 98.6 degrees to be the average. His data was valid at the time, so what changed?

The Old Average In 1851, Dr. Carl Reinhold August Wunderlich gathered statistical data on the temperatures of more than 25,000 patients. His research led him to conclusively say that the average human body temperature was 37 degrees Celsius (98.6 degrees Fahrenheit) and that a fevered state was defined as anything above 38 degrees Celsius (100.4 degrees Fahrenheit). He was the first to conclusively link illness with fever and to determine the average healthy temperature, which we have to this day called “normal.”

A Search For a New Normal

As early as the 1990s, researchers began questioning whether the accepted average was “normal” for everybody. That eventually led to a Stanford University study, which analyzed 650,000 readings from over 190,000 people.

The data showed the average temperature has been dropping slowly over the decades since Dr. Wunderlich’s study. Based on their research, the new average body temperature is 97.9 degrees Fahrenheit (36.6 degrees Celsius) for both men and women.

Possible Reasons For the Decline

So, what’s caused this decline in average body temperature? Dr. Julie Parsonnet, the senior author for the Stanford study, relayed several potential reasons for the decline.

People have become steadily healthier over the last 150+ years because of better nutrition, medical care and public health and sanitation. That, in turn, has resulted in us growing taller, gaining more weight and avoiding more infectious diseases because of vaccines and better treatments. We also control our home and office temperatures to around 68 to 72 degrees Fahrenheit year-round, so we avoid struggling to stay warm or cool down. We have less inflammation in our bodies than our ancestors did more than 150 years ago. Together, these factors could account for the drop in average body temperature.

What’s Your Average Body Temperature?

So what does this mean to you? Although the average normal body temperature is 97.9 degrees Fahrenheit, your individual normal average body temperature could be anywhere from 96.9 to 98.9 degrees Fahrenheit. Ideally, you can learn your normal by taking your temperature while you’re healthy. Take it at different times during the day and at different times of the month, then average the results to find out your normal.

By knowing your normal body temperature, you will be able to know when you are running a fever. Dr. Wunderlich defined fever as 1.8 degrees Fahrenheit (1 degree Celsius) above normal. That definition is still valid, but it should be applied to your normal body temperature. So if your normal is 97.9 degrees, fever might start at 99.7 degrees Fahrenheit for you.

While there are a number of possible reasons for the change, the takeaway is that your average temperature could vary slightly from the population average. But it does help to know, even in a general sense, that our body temperature has dropped and that a fever may be happening at a much different place than we once thought.

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