'Normal' human body temperature is a range around 98.6 F – a physiologist explains why

A salon owner scans a customer for a fever before performing a service. Bruce Bennett / Getty Images News about Getty Images
Fever is common in the symptomatic stage of COVID-19, and when workplaces and childcare facilities are reopened, temperature controls are one way officials try to identify those with the coronavirus. In order to maintain contactless conditions, many scan the skin temperature.
As warm-blooded animals, humans produce heat as a by-product of the chemical reactions that provide energy from the food we eat. It is this heat that keeps the human body in a fairly narrow range of "normal" body temperatures, and our biology works best in this small "normal" range.
But as a physiologist, I know that there are a variety of internal and external factors that can affect your temperature. "Normal" may be less universal than you think.
Normal, with some flex
Quick, what is a normal body temperature? You would almost certainly answer 37 degrees Celsius. Although this number is well known, the answer is actually more complicated.
Many attribute this number to a book on medical thermometry from 1871 by a German doctor named Carl Reinhold August Wunderlich, who measured the forearm temperatures of thousands of people. Readers appear to have removed the monolithic 98.6 number, but Wunderlich actually wrote that "healthy people in different conditions" had temperatures between 97.16 ° F and 100.4 ° F due to its measurement.
Even taking this deviation into account, a recent study found that core temperatures in the entire population were 0.3 ° C below the traditionally accepted values ​​and 0.5 ° C lower than in the beginning of the 19th century 20th century.
The researchers acknowledge that these reductions observed could be the result of changes in equipment and metrology. However, they suggest that the reduction could also reflect physiological shifts in metabolic rate and reductions in inflammation related to underlying diseases that treat people more effectively today than in the past.
A temperature reading depends on where you measure it on your body. Some of the most common places are in the mouth, in the ear, under the armpit, on the forehead or rectally. Each of these locations has slightly different normal values. Temperature measurements - such as oral or rectal - are carried out closer to places with higher energy consumption and generate more heat, which leads to higher temperature values.
Measurements in the body's own areas such as the ear or skin are influenced by the environment and tend to be lower. This is one of the reasons why skin temperature may not be a foolproof screening tool for COVID-19. Someone who is in a cool environment can mistakenly test for fever while someone who is out in the sun mistakenly tests for fever.
Keep your body warm and work
Body temperature is a by-product of your metabolism. Metabolism is the way your body converts fuel - the carbohydrates, fats and proteins from the food you eat - into usable energy. This process is only about 25% efficient. So when chemical bonds are broken, most of their energy is released as heat.
The body temperature is based on the warmth of your energy production. Food digestion, physical activity and infections increase metabolism and can raise your temperature.
Babies may have slightly higher normal body temperatures and calorie needs due to an increased metabolic rate to support growth and development, while seniors may have slightly lower body temperatures due to lower cell growth and repair rates.
In addition to changes that occur due to age, everyone varies throughout the day based on their daily rhythm. Both the 1871 book by Wunderlich and recent research have shown that people typically experience their lowest body temperatures overnight. Similarly, body temperature fluctuates in the different phases of the women's menstrual cycle.
When things get hot
Doctors generally classify fever as a temperature above 38 ° C, measured in both adults and children. Oral temperatures of 99.5 ° F and temperatures under the arm of 99 ° F are considered a fever in children.
While some are trying to reduce fever, higher temperatures seem to be an advantage in fighting infections and are actually part of your body's natural immune response. A possible physiological advantage is that fever prevents the replication of pathogens and can destroy them. Most human pathogens multiply best at temperatures below 98.6 ° F and have increasing problems as the temperature in your body rises.
Increased body temperature supports the body's immune system by increasing the activity of the cells and processes that identify, attack, and remove the intruders. Fever thus reduces the spread of the pathogen and at the same time increases the damage to the pathogens already present in the system.
Unfortunately, your organs also have preferred temperature ranges where they work properly. If your body temperature is too high, your own proteins and structures can be damaged. Such high temperatures can be fatal.
Exercise also increases your body's core temperature with increasing intensity. Increased energy production leads to increased heat gain in the body. When you are physically active, your muscles need extra energy to contract. In extreme cases, to run a marathon under two hours, Eliud Kipchoge required about 20 times more energy than when idle.
Environmental conditions such as temperature, humidity and wind play a role here. The body works best at moderate temperatures. However, people have got used to living in extreme situations with clothing and shelter. A cold environment can lead to an unsafe drop in body temperature. Hot and humid conditions can cause your body temperature to reach unsafe levels. Excessive body temperatures due to fever, intense physical activity, exposure to heat, or a combination can cause cell damage that can quickly lead to death.
Although everyone's body temperature is not necessarily 98.6 ° F, your “normal” value is still fairly close to that average. Humans live in a very narrow survival zone. Significant deviations from the average of these strictly controlled physiological variables can quickly become life-threatening.
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This article has been republished by The Conversation, a nonprofit news site dedicated to the exchange of ideas from academic experts.
Continue reading:
What the flu does to your body and why you feel so terrible
It is cold! A physiologist explains how you can keep your body warm

JohnEric Smith does not work for companies or organizations that would benefit from this article and does not consult any shares or companies that would benefit from this article and has not disclosed any relevant affiliations beyond her academic appointment.

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