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When we were students, we all learned a physiological knowledge in books: a person's average body temperature is 37 ℃.

However, in recent years, after the baptism of numerous temperature tests, we have found that the normal body temperature is often around 36.5℃, while more than 37 ℃ is considered to be hyperthermia.

Does this mean that a person's average body temperature is dropping?

(photo source: Gowling WLG)

In fact, the scientific community has long noticed this change.

Some scholars believe that in the past 20 years, the average body temperature has dropped to 36.6 ℃, and the body temperature is normal between 35.7 ℃ and 37.4 ℃.

Some scholars have studied the population oral temperature data from 1860 to 2017 and think that the new average body temperature should be 36.4 ℃.

In other words, more and more evidence shows that the average body temperature should be between 36.4 ℃ and 36.6 ℃.

Looking back in history, who set the figure of 37 ℃?

In 1851, Carl Wunderlich, a German doctor, published a book in which he claimed that he had visited 25000 patients and took their temperature millions of times. He averaged the data to 37 ℃.

Doctor ▲ was the first to propose that fever is not a disease, but a symptom. (photo source: Medical Eponym Library)

Now, many scholars speculate that the German doctor's data may be biased.

First of all, in an age when there were no computers, how did the doctor process millions of pieces of data and calculate the average? It doesn't seem reasonable.

Secondly, at that time, the axillary measurement was commonly used to measure the body temperature, which required the patient to hold the mercury thermometer under the armpit for 15 to 20 minutes, while sweating under the armpit, just after exercise, emotional excitement and other factors would affect the measurement results.

The rectal temperature is generally considered to be the most accurate for the normal body temperature range of different ▲ measurement methods. (photo source: Temp Pal)

In addition, the mercury thermometer used in that year is not accurate enough.

A mercury thermometer was kept in a museum in Philadelphia. Philip Mackowiak, a professor at the University of Maryland School of Medicine, borrowed a mercury thermometer and tested it and found it was about 0.8 ℃ higher than modern thermometers.

After all, in the 19th century, temperature measurement technology was not mature enough.

It can be seen that 37 ℃, the globally recognized average body temperature, may have been unreliable from the beginning.

▲ 19th century mercury thermometer. (photo source: sciencelearn.org)

So, is there a scientific basis for saying that the average temperature of the human body is declining?

To study this, a research team at Stanford University collected three sets of data.

The first set is the service records of the United States during the Civil War, as well as the medical records of veterans, spanning 1862-1930; the second set of data comes from a 1971-1975 survey conducted by the National Institutes of Health; the third set is data on adult patients at Stanford University Medical Center between 2007 and 2017.

(photo Source: reference [8])

Through a comparative analysis of the data, the researchers found that the body temperature of men born in the 1990s was generally about 0.59 ℃ lower than that of 19th century men, while that of women was about 0.32 ℃ lower.

On average, a person's body temperature drops by about 0.03 ℃ every ten years.

Interestingly, according to NASA, the average temperature of the earth has risen by about 0.6 ℃ in the past 100 years.

In other words, the earth is getting hot, but the human body is getting cold.

▲ the temperature of the earth is rising. (photo source: NASA)

As for why a person's average body temperature drops, there are several speculations in the scientific community.

First, people's metabolic level is declining. The so-called metabolism is that your body constantly exchanges matter and energy in order to maintain the normal operation of various systems, and heat is generated in this process.

In the past, due to poor health conditions, people are prone to inflammation, inflammation will speed up people's metabolism, leading to a rise in body temperature.

Nowadays, with the development of medical technology, human inflammation is reduced, and the body temperature naturally goes down.

Second, people's life is now more "constant temperature".

With heating in winter and air conditioning in summer, the body no longer needs to consume too much energy to regulate body temperature, so body temperature tends to be stable and lower at the same time.

▲ every household now has air conditioners. (photo source: DW)

Third, modern thermometers are more accurate.

Now we commonly use infrared thermometer and electronic thermometer. The forehead temperature gun used in public places is the infrared thermometer, because the skin temperature is measured, the error will be relatively large. The results of electronic thermometers are more accurate.

Traditional mercury thermometers are retiring from the stage of history. Due to the danger of mercury leakage after smashing, the State Drug Administration issued a document banning the production of mercury-containing thermometers and mercury-containing sphygmomanometers from January 1, 2026.

▲ traditional mercury thermometer. (photo source: pixabay)

Some people may ask, now that a person's body temperature has dropped, will the benchmark of "fever" change accordingly?

But for doctors, "fever" is actually difficult to define. At present, the standard adopted by the hospital is that an ear temperature of 38 ℃ is considered a "fever", but in practical application, there are too many complicated situations.

For example, people's body temperature in the morning is lower than at night; women's body temperature is higher during menstruation and pregnancy; body temperature is also related to age, and some elderly people do not have a "fever" at all, while babies above 37 ℃ are considered "feverish".

Therefore, there is no fixed value of body temperature even if it is "feverish".

The change in body temperature of ▲ people during the day. (photo source: clearvue health)

Although body temperature is only a number, it is a basic point for us to know and understand the human body.

Less than two hundred years have passed since the 19th century, when the German doctor who proposed 37 ℃ lived, but people's body temperature has really changed.

This shows that people are not immutable. The environment in which we live, our bodies, our temperature, are all adapting to each other, constantly adjusting, and changing dynamically.

"physically, we are not who we used to be."

Referenc

[1] What's the average human body temperature-and is it cooling down? National Geographic

[2] "Human Body Temperature Has Decreased In United States, Study Finds" 2020. Stanford Medicine News Center.

[3] "Time To Redefine Normal Body Temperature?-Harvard Health" 2020. Harvard Health.

[4] "Average Body Temperature Appears To Be Dropping. Researchers Aren'T Sure Why. 2020. Vox.

Doctors discuss new definition of 'fever' as average body temperature changes. 2022. Brussels Times.com

[6] "Fever In Babies" 2022. Webmd.

[7] "Student Video: NASA's Earth Minute: Earth Has A Fever" 2022. NASA/JPL Edu.

[8] Myroslava ProtsivCatherine LeyJoanna LankesterTrevor HastieJulie Parsonnet (2020) Decreasing human body temperature in the United States since the Industrial Revolution

This article comes from the official Wechat account: bring Science Home (ID:steamforkids), written by: Greye revision: Han Jingjing

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