Can you be “feverish” even if your thermometer reads as 98.6? The question is of particular interest now that we are approaching the flu season–not to mention the spiking cases of Covid.
New research suggests that the answer may be yes if your particular body temperature is normally as low as 97. That’s because what was the yardstick established in the 19th century, 98.6 as “normal”, may have been an erroneous theory from the start or may have changed over time.
According to a recent study published in JAMA Internal Medicine, the average body temperature of Americans has dropped by about 0.9 degrees Fahrenheit since the 19th century, when a German doctor, Carl Wunderlich, measured the armpit temperatures of about 25,000 people and came up with an average of 98.6 F. as the norm.
The researchers in the recent study analyzed data from more than 677,000 temperature measurements taken from 1896 to 2017 and found that the average body temperature declined by 0.05 degrees Fahrenheit per decade.
The reasons for this change are not fully understood, but some possible factors include better hygiene, lower metabolic rates, lower rates of infection and yes, even better thermometers.
Lower metabolic rates: your body uses energy so all your systems can work the way they should. This creates heat. But people may have lower metabolic rates now because we weigh more than people did centuries ago. The less heat your body makes, the lower your temperature.
Lower rates of infection: in the 19th century, infections such as tuberculosis, syphilis, and long-term gum disease were more common. As a result, many people had higher body temperatures.
Better thermometers: we may have more accurate thermometers than people did a century ago.
The study also suggests that body temperature is influenced by individual characteristics such as age, sex, height, weight, and time of day. Also that a “normal” body temperature can fall within a wide range, from 97 F to 99 F., and that it’s usually lower in the morning and goes up during the day. It peaks in the late afternoon or evening, sometimes by as much as 1 or 2 degrees. However, not all sources agree on this last factor. Webmd.com says that the outcome was not dependent on those factors, “A person’s age, gender, or weight didn’t make a difference, nor did the time of day.”
The authors of the new study recommend using personalized definitions of fever based on each patient’s baseline temperature rather than relying on a fixed cutoff point.
So how do you know if you have a fever?
Despite the new research, doctors still don’t consider you to have a fever until your temperature is at or above 100.4 F. But you can be sick if it’s lower than that.
