From 37 to 36.5 ℃, why is the human body getting colder?

  When we were students, we all learned a physiological knowledge in books: the average body temperature of a person is 37°C. However, in recent years, after experiencing numerous body temperature tests, we found that the normal body temperature is often around 36.5°C, and if it exceeds 37°C, it is considered to be a high body temperature. Does this mean that the average body temperature of people is constantly dropping?

  In fact, the scientific community has long noticed this change.
  Some scholars believe that in the past 20 years, the average human body temperature has dropped to 36.6 ℃, and the body temperature is normal between 35.7 and 37.4 ℃. Some scholars have also studied the oral temperature data of people from 1860 to 2017 and believe that the new average body temperature should be 36.4 ℃. That is to say, more and more evidence shows that the average body temperature of people should be between 36.4 and 36.6 ℃.
  Looking back on history, who set the data of 37℃? In 1851, a German doctor, Carl Wunderlich, published a book in which he claimed that he had seen 25,000 patients and took their temperatures a million times. He averaged these figures and it was 37°C.
  The doctor first proposed that fever is not a disease, but a symptom.

  Today, many scholars speculate that the German doctor’s data may be biased. First of all, how did this doctor process millions of data and calculate the average in those days when there were no computers? This doesn’t seem reasonable. Secondly, the armpit measurement method was commonly used to measure body temperature at that time. The patient was required to clamp the mercury thermometer under the armpit for 15 to 20 minutes. Factors such as sweating under the armpit, just finishing exercise, and emotional excitement would all affect the measurement results.

The normal body temperature range of different measurement methods, generally considered to be the most accurate rectal temperature

Body temperature change data

  In addition, the mercury thermometers used in those days were not accurate enough. In a museum in Philadelphia, the United States, a mercury thermometer of the year was preserved. Philip Mackowiak, a professor at the University of Maryland School of Medicine, borrowed the mercury meter and tested it, and found that it was about 0.8 ℃ higher than the modern thermometer. After all, in the 19th century, temperature measurement technology was not mature enough.

19th century mercury thermometer

  It can be seen that the globally recognized average body temperature of 37°C may be unreliable from the beginning.
  So, is there any scientific basis for saying that the average temperature of the human body is constantly falling? To investigate this, a team of researchers at Stanford University collected three sets of data.
  The first set is from service records during the American Civil War, as well as medical records of veterans, spanning the period 1862-1930; the second set of data comes from the results of the National Institutes of Health Survey 1971-1975; the third set is Adult patient data from Stanford University Medical Center 2007-2017.
  Through comparative analysis of the data, the researchers found that the body temperature of men born in the 1990s was generally about 0.59°C lower than that of men in the 19th century, and that of women was about 0.32°C lower. Calculated, the average body temperature of a person will drop by about 0.03 ℃ every ten years. Interestingly, according to NASA data, the average temperature of the earth has risen by about 0.6°C over the past 100 years. In other words, the earth is getting hotter, but the human body is getting colder.

Earth’s temperature is rising
Investigate the reasons for the drop in body temperature

  As for why the average body temperature of people drops, there are several speculations in the scientific community.
  One is that people’s metabolic level is declining. The so-called metabolism means that your body continuously exchanges substances 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 sanitary conditions, people were prone to inflammation, which would speed up people’s metabolism and lead to elevated body temperature. Nowadays, with the development of medical technology, people’s inflammation has been reduced, and the body temperature will naturally go down.
  Second, people’s lives are 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 the body temperature, so the body temperature tends to be stable and the body temperature is lower.
  Third, modern thermometers are more accurate.

Now every house has air conditioning

  Now we commonly use infrared thermometers and electronic thermometers. The forehead temperature gun used for temperature measurement in public places is an infrared thermometer. Since it measures the skin temperature, the error will be relatively large. The results of an electronic thermometer are more accurate. The traditional mercury thermometer is withdrawing from the stage of history. Due to the danger of mercury leakage after being broken, the State Food and Drug Administration issued a document that on January 1, 2026, the production of mercury-containing thermometers and mercury-containing sphygmomanometers will be banned.
  One might ask, now that a person’s body temperature has dropped, will the benchmark for “fever” change with it?
  For doctors, “fever” is actually difficult to define. At present, the standard adopted by the hospital is that the ear temperature reaches 38 ℃ even if it is “fever”, but in practical application, there are too many complicated situations. For example, people’s body temperature in the morning will be lower than at night; women’s body temperature is higher during menstruation and pregnancy; body temperature is also related to age, some elderly people do not have a “fever” at all, and a baby higher than 37 ℃ is considered “fever”. Therefore, there is no fixed value of how many degrees Celsius of body temperature is “fever”.

traditional mercury thermometer

Changes in human body temperature during the day

  Although body temperature is only a number, it is a basis for us to know and understand the human body. Less than 200 years have passed since the 19th century when the German doctor who proposed 37°C lived, but human body temperature has actually changed. This shows that people are not static. The environment in which we live, our bodies, and our temperature are all adapting to each other, constantly adjusting, and changing dynamically.
  ”Physiologically speaking, we are not what we used to be.”