From 37 to 36.5 ° C, why is the human body getting colder and colder?

(Picture source: Reddit)

Written article | GREYE

Audit | Han Jingjing

In the student days, we all studied a physiological knowledge in books: the average body temperature of a person is 37 ° C.

However, in recent years, after experiencing the baptism of countless body temperature testing, we found that normal body temperature is often around 36.5 ° C, while exceeding 37 ° C will be considered to be high in body temperature.

Does this show that the average body temperature is constantly declining?

(Picture source: Gowling WLG)

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

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

Some scholars have studied the temperature data of the population cavity from 1860 to 2017, and believe that the new average body temperature should be 36.4 ° C.

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

Back to history, who sets the data of 37 ° C?

In 1851, a German doctor Carl Wunderlight published a book. He claimed that he had diagnosed 25,000 patients and measured millions of body temperature for them.He took these data average, that is, 37 ° C.

The doctor first proposed that fever is not a disease, but a symptom.(Picture source: Medical eponym library)

Today, many scholars have speculated that the data of the German doctor may have deviations.

First of all, how did this doctor handle millions of data and calculate the average?This seems unreasonable.

Secondly, at that time, the measuring body temperature was generally used under the armpit measurement method, which requires patients to clamp the mercury thermometer for 15-20 minutes under the armpit, and factors such as sweat, just exercise, emotional excitement and other factors will affect the measurement results.

The normal body temperature range of different measurement methods is generally considered to be the most accurate at rectal temperature.(Picture source: TEMP PAL)

In addition, the mercury thermometer used that year was not accurate.

In a museum in Philadelphia, USA, a mercury thermometer was preserved. Philip Mackowiak, a professor at the University of Maryland Medical College, borrowed mercury and tested, and found that it was about 0.8 ° C higher than that of modern thermometers.

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

It can be seen that the global recognized average body temperature of 37 ° C may be unreliable from the beginning.

The 19th -century mercury thermometer.(Picture source:

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

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

The first set is the service record of the American Civil War, and the medical record of veterans, which spans 1862 to 1930; the second set of data comes from the survey results of the US National Health Investigation Agency from 1971 to 1975; the third set isData from adult patients from 2007 to 2017 at the Stanford University Medical Center.

(Image source: References [8])

Through the comparative analysis of data, researchers have found that men born in the 1990s are generally about 0.59 ° C lower than men in the 19th century, while women are about 0.32 ° C.

Calculated, the average body temperature every ten years will drop by about 0.03 ° C.

Interestingly, according to NASA data, the average temperature has increased by about 0.6 ° C 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.(Picture source: NASA)

As for why the average body temperature decreases, there are several speculations in the scientific community.

First, people’s metabolism levels are declining.The so -called metabolism is that your body continues to exchange material and energy in order to maintain the normal operation of each system, and heat will generate heat in this process.

In the past, due to poor hygiene conditions, people are prone to inflammation. Inflammation will accelerate people’s metabolism, resulting in an increase in body temperature.

Now with the development of medical technology, human inflammation has decreased, and body temperature naturally goes down.

The second is that people’s lives are now more "constant temperature".

There is heating in winter, air -conditioning in summer, and the body no longer needs to consume too much energy to regulate the body temperature. Therefore, the body temperature tends to stabilize and the body temperature is lower.

Now every family has air conditioners.(Picture source: DW)

Third, modern thermometers are more accurate.

What we often use now is infrared thermometer and electronic thermometer.The temperature gun used in public places is 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 exiting the stage of history.Since the leakage of mercury will be dangerous, the State Drug Administration issued a document, and the production of mercury -containing body thermometers and mercury blood pressure meters began on January 1, 2026.

Traditional mercury thermometer.(Picture source: Pixabay)

Some people will ask, since the body temperature is reduced, will the benchmark of "fever" change?

But for doctors, "fever" is actually difficult to define.At present, the standard adopted by the hospital is that the ear temperature reaches 38 ° C, even if it is "fever", but in practical applications, there are too many complicated situations.

For example, people’s body temperature will be lower than night; women have higher body temperature during menstruation and pregnancy; body temperature is also related to age. Some elderly people do not "fever" at all, and babies are higher than 37 ° C even "fever".

Therefore, there is no body temperature, even if the fixed value of "fever".

Human body temperature changes in the day.(Picture source: ClearVue Health)

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

In the 19th century where German doctors lived at 37 ° C, less than two hundred years have passed, but the human body temperature has actually changed.

This shows that people are not static.The environment for our lives, our body, and our temperature are all adapting to each other, constantly adjusting, and in dynamic changes.

"By physically speaking, we are no longer ourselves in the past."

Cover Source: Reddit

Reference materials:

[1] What’s the APrage Human Body Temperature —Ad is it cooling down? National Geographic

[2] "Human Body Temperature has decreased in united states, state finds". 2020. Stanford Medicine News Center.

[3] "Time to redefine normal body body? -Harvard Health". 2020. Harvard Health.

[4] "AVERAGE BODY TEMPERATURARS to Be Dropping. Researches are n’t sure why.". 2020. vox.

[5] Doctors discuss new definition of ‘fever’ as average body Temperature Changes. 2022. Brussels

[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 Lankester Hastiejulie ParsonNet (2020) DeCreasing Human Body Temperature Revolution

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