According to statistics from the Environmental Protection Agency (EPA), approximately 11,000 heat-related deaths occurred in the United States between 1979 and 2018. This number may even be higher as many areas do not report or recognize high temperatures as a cause of death.
How Does High Temperature Affect the Body?
High temperatures have numerous effects on human organs and can lead to death. Heat exhaustion and heat stroke are serious impacts caused by heat stress and can be fatal. High temperatures are also factors that exacerbate pre-existing medical conditions or cardiovascular diseases, including strokes and heart attacks.
High temperatures primarily harm the human body due to dehydration. The body’s water balance mechanism is temperature-dependent and interacts significantly with the surrounding air through the skin and respiration.
In hot weather, especially dry heat, water evaporates through the skin and the respiratory process at a rate that the body cannot compensate for quickly enough. Evaporating sweat cools the body, but excessive sweating can lead to dehydration.
According to the Centers for Disease Control and Prevention (CDC), over the past 13 years, high temperatures have ranked above storms and tornadoes, becoming the leading cause of weather-related deaths.
Rehydration is the best way to regulate body temperature.
The water balance mechanism is crucial for internal organs and cellular function. Dehydration leads to a decrease in blood volume and stifles activity, causing damage or loss of function in organs, potentially resulting in cell death. Inadequate blood circulation hinders the supply of essential oxygen needed for organs to function, which is why the rate of cardiovascular diseases increases during hot weather.
Additionally, body temperature is also influenced by blood circulation. Reduced blood circulation is akin to starting a car with an empty gas tank. Blood circulation is one of the primary and sole mechanisms for maintaining appropriate internal body temperature. During respiration, the body inhales outside air that is generally cooler than the internal body temperature, which lowers the blood temperature as it enters the lungs to take in oxygen, helping regulate body temperature.
What Are the Limits of Human Heat Tolerance?
According to a report published in the 2021 Journal of Physiology, the temperature limit at which the human body can maintain activity and balance is around 40-50 degrees Celsius. When air temperature reaches 50 degrees Celsius, our bodies cannot dissipate heat anymore, and body temperature will rise. However, another study cites a much lower threshold of 32 degrees Celsius—the temperature at which humans begin to sweat. Besides air temperature, humidity also plays a significant role; the higher the humidity, the harder our bodies must work to stay cool.
Another widely recognized study states that a person can die if standing for 6 hours in an environment with a wet-bulb temperature of 35 degrees Celsius (equivalent to 35 degrees Celsius at 100% humidity, or 46 degrees Celsius at 50% humidity).
The wet-bulb temperature is a measurement that accounts for both temperature and humidity, where water vapor has saturated the air, according to research published in the Journal of Applied Physiology.
In such situations, when in an environment with both high humidity and temperature, humans will find it harder to sweat, while sweating helps reduce about 80% of heat in the body. This inability to dissipate heat can lead to overheating, causing respiratory and cardiovascular issues, even death.
However, it is not necessary to reach the wet-bulb temperature limit for hot weather to pose health risks. The World Health Organization (WHO) states that increased temperatures will expose the body to hotter than normal levels, affecting heat adaptation abilities and possibly causing conditions like heat stroke, exhaustion, and hyperthermia.
Extreme temperatures can also exacerbate chronic illnesses, including cardiovascular, respiratory, cerebrovascular diseases, and diabetes-related conditions.
The high-risk groups most affected by heat include the elderly, infants and children, pregnant women, outdoor workers and laborers, and athletes…
Residents of Bangkok, Thailand walking under the scorching sun on April 15. (Photo: Bangkok Post).
The temperature limits within the body are even more restrictive. According to MedlinePlus, brain damage can occur when internal body temperature reaches 42 degrees Celsius.
In a 2022 article in Outside Magazine about heat stroke, it cites the highest temperature at which humans can survive: “The highest internal temperature that the organs can withstand is only about 8.3 degrees higher than normal body temperature. Willie Jones, a 52-year-old man from Atlanta, was rescued from his apartment during a heat wave in 1980 with an internal body temperature of 46.5 degrees Celsius.” The article also mentions that the lowest temperature that human organs can tolerate is 13.7 degrees Celsius. Low temperatures slow blood circulation, which can lead to severe damage in cold weather, such as frostbite. Without blood to warm tissues, those tissues freeze, and ice crystals can damage cells and tissues.
These figures provide a meaningful visual context as we now understand the impact of temperature on evaporation rates. As body temperature decreases, it can lead to various problems but does not result in dehydration. In fact, medical researchers are exploring a new technology called emergency preservation and resuscitation, where patients are cooled intravenously to 10 degrees Celsius to slow blood loss during emergency surgery due to trauma.
How to Manage Heat Stress
Currently, humans cannot do much to adapt to high temperatures other than maintaining hydration. When sweating, the body loses a significant amount of salt and minerals. If one only drinks plenty of water without replenishing the depleted minerals, complications may arise. According to the CDC, to mitigate the effects of high temperatures, we should cool down in our living spaces, such as taking cool showers, eating cold foods, and wearing lighter clothing.
It is worth noting that electric fans do not prevent heat-related illnesses. In fact, due to the evaporation process, under the same temperature conditions, a person may lose more water if a fan is running. The wind carries water vapor away faster because the heavier water particles are blown away.
As the climate warms, humans will need to adapt to survive. The year 2023 has been recorded as the hottest year globally, and residents in Phoenix, Arizona, experienced 31 consecutive days with temperatures reaching as high as 43 degrees Celsius. As climate change continues, especially if governments worldwide do not take action against it, there will be more climate refugees, and some regions like Arizona may become uninhabitable.
It is incredibly challenging for the human body to manage simple biological phenomena of heat and evaporation to cope with the rapidly warming environment. Since the bodies of most organisms rely on maintaining moisture balance, the impact of high temperatures could lead to the next mass extinction event on Earth. It is time to “accelerate” efforts to prevent and reverse climate change.
