The human body cannot handle large variations in its internal temperature. At 42ºC, just 5 degrees above normal, the proteins start to cook and the whole organism breaks down. Already the cold makes the metabolism decrease, but it is not as fatal as the heat. The thermometer needs to go down to 20°C for irreversible cardiac arrest to occur.
But well before these extreme limits, the body starts to react. “At 40ºC, the so-called hyperthermia (excess heat) begins and at 35ºC, hypothermia (lack of heat)”, says physiotherapist Sérgio Cravo, from the Federal University of the State of São Paulo (Unifesp). To avoid abrupt variations, the body has a series of mechanisms to keep the internal temperature constant, regardless of the climate. To contain the heat, the main mechanism is perspiration. Sweat lowers the temperature because, to evaporate, it removes heat from the skin, refreshing it.
In humid environments, perspiration evaporates with more difficulty, so we feel higher temperatures more. To face the cold, one of the body’s tricks is to make the person shiver, which helps to produce heat internally. But it is clear that in extreme situations these mechanisms do not work. In the book Life on the Edge – The Science of Survival, British physiologist Frances Ashcroft talks about the body’s reaction to threshold environmental temperatures. According to her, the mark of -29 ºC, which would be bearable with appropriate clothing, can become fatal if added to a wind of 40 km/h, which would produce a thermal sensation equivalent to -66 ºC, enough to freeze the meat in 30 seconds. Already in the heat, the survival record is 20 minutes at 127 ºC, in dry air.
In the end, the resistance capacity of the human body depends on the external temperature, humidity, wind, time of exposure to the environment and even the fact that the person is immersed in water. As the water cools down quickly, it is enough for someone to be immersed at around 20ºC to run the risk of dying.
From fever to chills
Organism resists the fall more than the increase in internal temperature
42°C
The body is literally close to cooking and the functioning of the organs and the entire metabolism is affected. The person can go into a coma. At this temperature, there are no longer any guarantees that life can be saved.
40°C
Here begins hyperthermia (excess heat). The loss of fluid and mineral salts causes dizziness, nausea and vomiting, confusion and loss of consciousness. At this point, the person may even stop sweating, a sign that they are dehydrated.
38°C
In a feverish state, the person begins to sweat a lot, feel muscle spasms and exhaustion. The pulse becomes weak and fainting may occur. The recommendation is to avoid the sun, splash cold water on the body and drink a cold non-alcoholic drink.
36.5 to 37.5°C
normal body temperature
35°C
Here begins hypothermia, or excessive heat loss. The person feels chills, fatigue, apathy and loses a little motor coordination. Thinking is slowed down and judgment is impaired—the person may be uncooperative with those trying to help him or her
30°C
At this level, blood flow in the brain decreases, causing mental confusion and reasoning problems. The heart rate may reach a rate of only one or two beats per minute, in which case the person appears to be dead.
20°C
As body temperature drops, metabolism slows down more and more, until the heart stops and brain activity ceases altogether. A body with an internal temperature of 20°C cannot live longer