Many people think normal body temperature is 37°C. This number came from a German doctor about 150 years ago. Today, a study of about 35,000 people found that the average was 36.6°C. Also, each person has a different normal temperature.

Older people are a little cooler. So it is a good idea to check your own temperature when you are healthy.

Doctors have long treated 37°C as normal body temperature. That number comes from a German doctor in the 19th century. Modern studies show that most people are usually a little cooler.

In 2017, researchers analyzed about 240,000 temperature readings from 35,488 patients without infections at an American hospital. The average was 36.6°C, and 95 percent of people were between 35.7°C and 37.3°C. Older people were also slightly cooler than younger people.

Another study, in 2020, compared records from three different periods in the United States. It found that body temperature has dropped by about 0.03°C for each decade of birth. Nobody knows exactly why. One possible reason is that people today get fewer infections than people did in the past.

When doctors call 37°C (98.6°F) "normal," they are repeating a figure from Wunderlich, a 19th-century German physician who popularized temperature as a sign of disease. Modern data put the number slightly lower. In 2017, a team led by Harvard researchers examined roughly 240,000 measurements from 35,488 outpatients with no diagnosed infection.

The mean was 36.6°C, and 95 percent of individuals fell between 35.7°C and 37.3°C. Temperature declined a little with age, and each person seemed to have a characteristic baseline of their own. Where the thermometer goes also matters. A 2019 systematic review found that armpit readings run lower than oral ones.

The longest view comes from a 2020 Stanford study, which compared records from Civil War veterans, a 1970s national survey and recent medical data. Body temperature had fallen by about 0.03°C per birth decade. The authors could not fully rule out changes in thermometers and measurement sites across those eras. Their proposed explanation is that less infection and inflammation, along with heating and cooling, may have changed human metabolism.