Humans' heat tolerance limit is not as high as we think

According to statistics from the EPA, about 11,000 deaths in the US were caused by heat waves in the period from 1979 to 2018. This number could be even higher because many places do not list or recognize high temperatures as a cause of death.

How does high temperature affect the body?

High temperatures cause many effects on organs in the human body and can lead to death. Exhaustion and heat stroke are serious effects caused by heat stroke and can lead to death. High temperatures are also known to aggravate certain pre-existing medical conditions or cardiovascular disease, including stroke and heart attack.

High temperatures damage the human body mainly because of dehydration. The human body's water balance mechanism depends on temperature and highly interacts with the air environment around the body through the skin and the respiratory process.

In hot weather, especially hot dry weather, water evaporates through the skin and the respiratory process is so fast that the body cannot compensate in time. Evaporating sweat cools the body, but losing too much sweat will lead to dehydration.

According to the US CDC, over the past 13 years, high temperatures have ranked above hurricanes and tornadoes, becoming the leading cause of weather-related deaths.

Hydration is the best way to balance body temperature.

The water balance mechanism is very important for internal organs and the functioning of cells. Lack of water will lead to reduced blood volume in the body and stagnation of activity, causing damage or loss of organ function, and even causing cell death. Insufficient blood circulation hinders the supply of essential oxygen for organs to function, which is why the rate of cardiovascular disease increases in hot weather.

Besides, body temperature is also affected by blood circulation . Impaired blood circulation is like starting a car with no oil. Blood circulation is one of the main and only mechanisms for maintaining the right temperature inside the body. When breathing, the body receives outside air that has a lower temperature than inside the body and reduces the temperature of the blood entering the lungs to get oxygen, contributing to regulating body temperature.

What is the limit of human heat tolerance?

According to a report published in Physiological Reports 2021, the temperature limit at which the human body can maintain activity and balance is between 40-50 degrees Celsius . When the air temperature reaches 50 degrees Celsius, our body can no longer dissipate heat and our body temperature will increase. But another study cited a much lower limit of 32 degrees Celsius - the temperature at which humans start to sweat. In addition to air temperature, humidity also plays a big role, and the higher the humidity, the harder our bodies have to work to stay cool.

Another more widely recognized study is that a person can die if standing for 6 hours in a wet-bulb temperature environment of 35 degrees Celsius (equivalent to 35 degrees Celsius with 100% humidity, or 46 degrees Celsius). degrees Celsius and humidity 50%).

Wet bulb temperature is a measurement method that takes into account both temperature and humidity, where water vapor is saturated in the air, according to research published in the Journal of Applied Physiology.

With such a condition, when in an environment where both humidity and air temperature are high, it will be more difficult for people to sweat, while sweat helps reduce about 80% of body heat. This prevents the body from escaping heat, leading to overheating, causing respiratory and cardiovascular problems, and even death.

However, there does not need to be a critical level of wet bulb temperature for hot weather to cause health risks. The World Health Organization (WHO) said that increased temperatures will expose the body to hotter than normal heat , affecting the ability to adapt to heat and can cause conditions such as heat stroke and exhaustion. and increased body temperature.

Extreme temperatures can also worsen chronic diseases, including cardiovascular, respiratory, cerebrovascular and diabetes-related diseases.

High-risk groups most affected by heat include the elderly, infants and children, pregnant women, outdoor and manual workers, athletes.

People in Bangkok, Thailand walk under the hot sun on April 15. (Photo: Bangkok Post).

The body's internal temperature limits are even more restrictive . According to MedlinePlus, brain damage can occur when the body's internal temperature reaches 42 degrees Celsius.

A 2022 Outside Magazine article on heatstroke cites the highest temperature a human can survive: ' The highest temperature the body's internal organs can withstand is only about 8.3 degrees higher than with normal temperature. Willie Jones, a 52-year-old Atlanta man, was rescued from his apartment during a 1980 heat wave with an internal body temperature of 46.5 degrees Celsius . Also according to the above article, the lowest temperature that organs inside the human body can withstand is 13.7 degrees Celsius . Low temperatures slow blood circulation, which can cause serious cold weather injuries such as frostbite. Without blood to warm the tissue, the tissue will freeze and those ice crystals will damage cells and tissue.

These are figures that make intuitive sense because we now understand the effect of temperature on the rate of evaporation. As the body temperature gets lower and lower, it causes various problems but does not lead to dehydration. In fact, medical researchers are exploring a new technology called emergency preservation and resuscitation, in which patients are cooled intravenously to 10 degrees Celsius to slow blood loss. while they underwent emergency surgery for their injuries.

Ways to control heat stroke

Currently, people still cannot do much to adapt to high temperatures other than keeping their bodies hydrated. When you sweat, your body loses a lot of salt and minerals. If you only drink a lot of water but do not replenish the depleted minerals, the body may experience other complications. According to the US CDC, to limit the effects of high temperatures, we should reduce the temperature in our home, such as taking cool baths, eating cold foods and wearing thinner, lighter clothes.

Notably, electric fans do not prevent diseases related to high temperatures . In fact, due to evaporation, a person can lose more water under the same temperature conditions than if a fan is running. Wind carries water vapor faster because the heavier water particles themselves will be blown away by the wind.

As the climate warms, humans will have to adapt to survive. 2023 is the hottest year on record in the world, and residents of the Phoenix, Arizona area have experienced 31 consecutive days of low temperatures of 43 degrees Celsius. As climate change continues, especially if the If governments around the world do not fight back, there will be more climate refugees and some places like Arizona may no longer be suitable for human habitation.

It is difficult for the human body to control the simple biological phenomena of heat and evaporation to accommodate a rapidly warming environment. Because the bodies of most organisms rely on maintaining moisture balance, impacts from high temperatures could lead to the next mass extinction event on Earth. It is time to 'accelerate' efforts to stop and reverse climate change.