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The "New Normal" for Body Temperature

Primary Care Wellness Healthy Aging
Reading a digital thermometer

All our lives, we’ve considered 98.6 degrees Fahrenheit to be normal body temperature. This number was calculated by a German physician in the mid-1800s based on an average of the temperatures of 25,000 patients. However, if you’re healthy and have seen a doctor lately, chances are you were told your temperature was less than 98.6 degrees.

“In fact, there are several newer studies that indicate body temperature has decreased over time,” says Lisa C. Jenkins-Haynie, M.D., a family medicine physician with Riverside’s White Stone Family Practice.  “Current research indicates a more accurate number is in the 97.5 - 97.7 degrees range.” A research article on decreasing human body temperature in the United States since the Industrial Revolution supports this finding.

The question is, why?

The evidence

The first thing that must be addressed is whether the measurements from 1851 were accurate. It’s important to note that in those times, life expectancy was quite short, and many people had untreated infections like gum disease, tuberculosis and syphilis, all of which could have caused persistent fevers. 

In addition, in the 1800s, temperatures were usually taken under the arm rather than by mouth, and thermometers then were probably not as accurate as those made today, so the data may have been skewed when compared to that collected by modern measurement methods.

Later studies done during the Civil War, in the 1970s and in the 2000s support a lower number. This may be due to several different factors:

  • Better health care, resulting in lower rates of infection and inflammation than were common in the 1800s
  • A decrease in metabolic rate that may be due either to people being heavier now, or changes in lifestyle over time
  • The increased use of anti-inflammatory drugs like aspirin and ibuprofen that tend to lower temperature
  • More widespread use of heating and air conditioning, which helps reduce metabolic level, and along with it, body temperature

Temperature variation

Different people have different temperatures that are normal for them. However, individual body temperature goes up and down throughout the day. It’s at its lowest early in the morning and tops out in late afternoon. 

According to a study on the influence of gender and race on mean body temperature in a population of healthy older adults, temperature also varies by age, gender and ethnicity. Women in their reproductive years tend to be a bit warmer than men, although among older white individuals, men and women have about the same temperatures. Older Black women run a slightly higher temperature than their white counterparts. 

According to Medical News Today, the normal temperature in babies tends to be higher than adults because they don’t sweat much and tend to retain more body heat.

Should you worry?

Body temperature can become too low, resulting in hypothermia, which can cause the body’s systems to shut down. However, a far more common problem is a temperature that’s too high.

Dr. Jenkins-Haynie says, “A fever is still considered to be any temperature over 100.4 degrees. This usually indicates infection or another health condition that needs to be checked out. A high fever can be quite serious.”

There is some current thinking that if the normal body temperature is lower than previously believed, the threshold for fever may need to be adjusted downward as well. However, many people can tell if they have a fever just by how they feel—weak, chilled, but with skin warmer than usual to the touch. 

Because temperature is an indicator of health, your doctor will measure it whenever you visit. If you haven’t had a physical in the past year, schedule an appointment today.

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