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Have you ever gone to the doctor because you were pretty certain you were coming down with something and you felt like you had a low-grade fever only to be told your temp is “normal?”  Or, have you taken your child’s temp and found the thermometer to read the standard average of 98.6 degrees, but you know that your little one really is a little too warm?

Well, you’re raised eyebrows may be attached to an actual hypothesis.

It seems that we’re getting colder, or at least a little cooler, according to Stanford University School of Medicine researchers. They have determined that within the United States, the average body temperature has decreased since the 1800s. Meaning that the “normal” human temperature of 98.6 degrees Fahrenheit (or 37 degrees Celsius) is too high. In fact, Julie Parsonnet, MD, professor of medicine and of health research and policy says, “Our temperature’s not what people think it is…What everybody grew up learning, which is that our normal temperature is 98.6, is wrong.”

German physician, Carl Reinhold August Wunderlich, was the first to publish the standard figure 

of 98.6 in a book back in 1868. Recent studies have called that standard into question. One such 2017 study found that the average temperature among 35,000 British patients to be 97.9 F.

In this most recent study, posted in eLife, Parsonnet and her colleagues explore body temperature trends and conclude that temperature changes since the time of Wunderlich indicate a true pattern, rather than measurement errors or biases. The researchers propose that the decrease in body temperature is the result of changes in our environment over the past 200 years, which have in turn driven physiological changes.

For this study, Dr. Parsonnet and her colleagues analyzed temperatures from three datasets covering distinct historical periods. The earliest set, compiled from military service records, medical records, and pension records from Union Army veterans of the Civil War, captures data between 1862 and 1930 and includes people born in the early 1800s. A set from the U.S. National Health and Nutrition Examination Survey I contains data from 1971 to 1975. Finally, the Stanford Translational Research Integrated Database Environment comprises data from adult patients who visited Stanford Health Care between 2007 and 2017.

With that data, they used the 677,423 temperature measurements to develop a linear model that determined temperature over time. The model confirmed body temperature trends that were known from previous studies, including increased body temperature in younger people, in women, in larger bodies and at later times of the day.

What they found was that the body temperature of men born in the early to mid-1990s is on average 1.06 F lower than that of men born in the early 1800s. Likewise, they determined that the body temperature of women born in the early to mid-1990s is on average 0.58 F lower than that of women born in the 1890s. These results found a decrease in body temperature of 0.05 F every decade.

It may be time to reexamine our methods and policies about measuring fevers. We need to start listening to our bodies’ natural responses. We need to listen and pay attention to our children when they aren’t feeling well. At any rate, we need to trust ourselves when we know something is off. It may not be us. It’s probably our thermometer!