With climate change causing temperatures to rise across the globe, extreme heat is increasingly becoming a health threat. The human body is resilient, but it can’t do that much. So what is the maximum temperature the human body can withstand?
The maximum temperature that the human body can withstand
The answer is relatively simple, according to a study conducted in 2020. The maximum temperature that the human body can withstand is 35 degrees Celsius, which is the wet bulb temperature. The wet bulb temperature is not the same as the air temperature you might see reported by your local forecaster or your favorite weather app.
Rather, a wet-bulb temperature is measured by a thermometer covered with a cloth soaked in water and takes into account both heat and humidity. The latter is important because if there is more water in the air, it is harder for sweat to evaporate from the body and cool a person.
If the humidity is low but the temperature is high , or vice versa, the wet bulb temperature probably won’t approach the tipping point of the human body, said Colin Raymond, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory who studies extreme heat. But when both humidity and temperature are very high, the wet bulb temperature can creep into dangerous levels.
For example, when the air temperature is 46.1 C and the relative humidity is 30%, the wet bulb temperature is only about 30.5 C. But when the air temperature is 38.9 C and the relative humidity is 77%, the wet bulb temperature is about 35 C.
If the wet bulb temperature is increased, then the internal temperature can no longer be adjusted
The internal temperature can no longer be adjusted
The reason humans cannot survive in high heat and humidity is that they can no longer regulate their internal temperature. At this point, the body becomes hyperthermic — above 40 C. This can lead to symptoms such as a rapid pulse, a change in mental status, a lack of sweat, fainting and coma, according to the National Institutes of Health.
However, a wet bulb temperature of 35 degrees Celsius will not cause immediate death; it probably takes about 3 hours for that heat to become unbearable. There’s no way to know for sure the exact duration, but studies have tried to estimate it by immersing human participants in tanks of warm water and removing them when their body temperature began to rise uncontrollably.
There is also no way to confirm that this is the exact wet bulb temperature, a temperature at which the human body cannot survive. Raymond estimated the true number to be in the range of 34 C to 36.5 C. Although no one can live at a wet-bulb temperature above about 35 C, lower temperatures can also be deadly.
Exercise and exposure to direct sunlight make it easier to overheat. Few locations have reached a wet-bulb temperature of 35 C in recorded history, according to the Science Advances study. Since the late 1980s and 1990s, the hotspots have been in central and northern Pakistan and the southern shores of the Persian Gulf.
“There are places that are already starting to experience these hour or two conditions, and with global warming, it’s going to become more common,” Raymond said.
Locations at risk of these temperatures over the next 30 to 50 years include northwestern Mexico, northern India, Southeast Asia, and West Africa.
