My temperature has been taken a lot lately as I am sure is the case with you as well. I’ve noticed that I usually run just a bit over 97° and it sometimes is 96 point something degrees. Having been told throughout my life that the average normal body temperature is 98.6°, I wondered if I am abnormally cool. Nope. It turns out that 98.6° is no longer considered the average normal body temperature.
Why Was 98.6° Considered Normal?
In the mid-1800s the German physician Carl Reinhold August Wunderlich recorded over 1 million temperatures of 25,000 generally healthy people. Based on all these temperature readings he concluded that the average normal body temperature was 98.6° Fahrenheit (37° Celsius). While differences where the temperature is taken (orally, armpit, or rectally) or the type of instrument used can affect temperature readings, modern experts think that Dr. Wunderlich’s observations were likely correct and 98.6° was a pretty good estimate of body temperature for the population as a whole.
Human Body Temperature is Decreasing
Over two dozen studies have concluded that 98.6° is now too high and that the normal body temperature is now about 97.5°. A study published in January by researchers at Stanford University analyzed nearly 700,000 temperature readings over a span of 157 years and concluded that the average normal human temperature is decreasing.
Here’s a chart of temperatures collected over a recent 10-year time period — note that most temperatures were well below 98.6°.
Why Has Body Temperature Been Decreasing?
Medical experts aren’t sure why body temperatures have been dropping, but they have some good guesses.
Body temperature is a proxy for metabolic rate and provides a window into overall health. The decline in average body temperature over the past 160 years reflects a drop in metabolic rate which likely means that humans are healthier now than in the past. From the Stanford Study:
Although there are many factors that influence resting metabolic rate, change in the population-level of inflammation seems the most plausible explanation for the observed decrease in temperature over time. Economic development, improved standards of living and sanitation, decreased chronic infections from war injuries, improved dental hygiene, the waning of tuberculosis and malaria infections, and the dawn of the antibiotic age together are likely to have decreased chronic inflammation since the 19th century. For example, in the mid-19th century, 2–3% of the population would have been living with active tuberculosis.
Basically, healthier bodies have less inflammation and inflammation often causes an increase in temperature.
Another possible reason is that modern heating and cooling assist our bodies in maintaining a healthy temperature. The Stanford study noted that “Maintaining constant body temperature despite fluctuations in ambient temperature consumes up to 50–70% of daily energy intake.” Thus, our bodies don’t have to work as hard to regulate temperature in modern times which may result in a lower metabolic rate, which in turn translates into lower average body temperature.
Also, modern drugs such as ibuprofen and aspirin can help control inflammation and thus lead to lower temperatures. The introduction and popularity of these drugs could be a reason for lower temperatures.
Our Individual Temperature Fluctuates
A word of caution about new average temperature being 97.5°: each of us has our own baseline normal temperature and what might be a bit high for one person can be normal for another. According to Dr. Donald Ford of the Cleveland Clinic:
Typically anything in the range of 97 to 99 degrees Fahrenheit is considered normal, but there are times when a perfectly healthy person might have a body temperature that’s slightly higher or slightly lower than that.
Another important point is that even an individual’s temperature varies widely, by about 1.8°F, throughout a 24-hour cycle. Your temperature is usually at its lowest a few hours before you wake up and is at its highest the few hours before bed. Related: Why Do Humans Love To Sleep With Blankets?
Age plays a factor in our personal average temperature as well: research has found that our temperature drops about 0.03° per decade of life.
The main takeaway is that each of us has our own baseline temperature and on average it’s closer to 97.5° than 98.6°, but our own temperature varies throughout the day.