As climate change rises around the world, extreme heat is becoming more common and therefore a greater threat to health. The human body is resilient, but can only handle it that much. So, what are the highest temperatures people can withstand?
According to a 2020 survey by Journal Science Advances, the answer is simple. The temperature of the wet bulb is not the same as the temperature reported by local meteorologists and favorite weather apps. Rather, wet bulb temperatures are measured using a thermometer covered with a cloth soaked in water, and the resulting metrics take into account both heat and humidity. The latter is important. This is because when there is too much water in the air, sweat evaporates from the body, making it difficult to cool people down.
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For example, if the temperature is 115 F (46.1 C) and the relative humidity is 30%, the wet bulb temperature is only about 87 F (30.5 C). However, when the temperature is 102 F (38.9 C) and the relative humidity is 77%, the wet bulb temperature is about 95 F (35 C), which is a human “danger zone.”
The reason people can’t survive high heat and humidity is because they can no longer regulate the internal temperature. “If the temperature of the wet bulb exceeds the human body temperature” – about 98.6 F (37 C) – “You can still sweat, but you can’t cool your body to the temperature that requires physiological operation,” Raymond told Live Science.
At this point, the body will be at a high temperature and experience a thermal stroke at an internal temperature above 104 F (40 C). This can lead to symptoms such as rapid pulse, confusion, delirium, itching, blurry and coma, according to the Cleveland Clinic.
However, a wet bulb temperature of 95 F does not die immediately. Raymond said it would probably take about three hours for that fever to kill you. There is no way to know the exact time for sure, he said – although some studies have tried to estimate it, it is not ethical to actually impose humans on such high temperatures for hours.
There is also no way to ensure that 95 F is the exact wet bulb temperature. Raymond estimated that the true numbers are somewhere in the range of 93.2 f to 97.7 f (34 c – 36.5 c).
Who is at risk of temperature?
Air conditioners can save people from the heat of blame, but not everyone has access to it, and even in places where many people have air conditioning, electric grids may not be reliable, Raymond said.
Research by Science Advances shows that in recorded history, several locations have reached wet bulb temperatures of 95 F, but have only been there for a short period of time. From the late 1980s and late 1990s, hotspots have been in the Indus River Valley in central and northern Pakistan, and the south coast of the Persian Gulf.
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Pakistan’s Jacobad is sometimes called the hottest city in the world, and has surpassed wet bulb temperatures at least four times, surpassing cities, including La Paz, Mexico. Port Hedland, Australia. Abu Dhabi, United Arab Emirates, records temperatures above 90 F (32 C) wet bulbs.
“We already have places where we are beginning to experience these conditions for an hour or two,” Raymond said. “And with global warming, it’s only going to be more frequent.” Regions at risk for these temperatures over the next 30-50 years include northwest Mexico, northern India, southeast Asia and West Africa.
“Unfortunately, with climate change already trapped, it will continue to be quite warm even if we stop today’s greenhouse gas releases,” Raymond said. “I think it’s inevitable that the places I mentioned will be addressing this issue in the near future, and I hope that more places don’t add to that list.”
The “power multiplier” of illness
Some researchers argue that the 95 F wet bulb threshold actually underestimates the high temperature risks of human health.
Pope Moseley, a researcher at Arizona State University studying fever-related illnesses, warns that it focuses on the maximum temperature a person can handle under optimal conditions. The reality is that factors such as age, physical fitness, certain medications, and health conditions can all limit your ability to cope with fever even when temperatures are low.
For example, exercise or exposure to direct sunlight makes it more likely to overheat at low temperatures. Elderly; people with certain health conditions, such as hormonal disorders and obesity. People taking antipsychotics are also more vulnerable to heat-related deaths, as they are unable to regulate temperatures.
Moseley gives examples of young fit people with older people with heart failure and dementia who forget to drink water. “The maximum survival limits for these two people look very, very different,” he warned.
Moreover, fever-related deaths and illnesses are not always easy. Mosely said that many deaths during the heat wave may not be recorded as primarily heat-related.
High temperatures can exacerbate many medical problems. For example, fever can affect blood vessel constriction, which can exacerbate hypertension and other heart problems. People with kidney disease are at risk because they affect the fluid levels that people with kidney disease need to strictly regulate. Additionally, some severe mental illnesses can affect a person’s ability to recognize early signs of heat stress and can be at risk for heat waves. Other conditions that can be exacerbated by fever include diabetes, asthma and dementia.
Because of these connections, Moseley calls fever the “multiplier of the force of disease.” This is a factor that exacerbates many other conditions. Therefore, the real effects of heat are actually much broader, and many people can face fatal health problems at wet bulb temperatures much lower than 95 F.
“Before that, there are a lot of people who suffer from catastrophic illnesses,” Moseley said.
This article is for informational purposes only and is not intended to provide medical advice.
Editor’s Note: This article was originally published on July 31, 2021. Updated September 25, 2025, it contains detailed information on the possibility that high temperatures and wet bulb heat around the world can become the “force multiplier” of diseases.
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