# What heat-humidity combination will eventually kill you? **URL:** \ **Category:** Factual Questions\ **Created:** [August 30, 2025, 9:10pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617 "2025-08-30T21:10:55Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\ **Post date:** [August 30, 2025, 9:10pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/1 "2025-08-30T21:10:55Z")
It seems just being out in X temperature, Y percent humidity is enough to kill you, sooner or later. Your body can’t cool itself, even if you’re just sitting around, and eventually your body temperature gets too high. What air temperature would be enough to kill lots of people (in an hour or two, say) if the humidity were 90%? Would dropping to 80% make a big difference? ---
**Author:** ![DMC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dmc/32/18049_2.png) [@DMC](https://boards.straightdope.com/u/DMC)\ **Post date:** [August 30, 2025, 9:48pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/2 "2025-08-30T21:48:18Z")
There are way too many variables to give an exact answer, but the following is probably close enough. At 90% humidity, 92 degrees or so puts you in the extreme danger category for heat stroke if you stay in that environment and do physical activities. Dropping to 80% humidity isn’t that big of a difference. At that level 94 degrees has approximately the same heat index as above. ---
**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\ **Post date:** [August 30, 2025, 9:50pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/3 "2025-08-30T21:50:43Z")
Too many variables person to person, you mean? Or you mean this 90% humidity is worse than that 90% humidity? ---
**Author:** ![DemonTree](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/demontree/32/8646_2.png) [@DemonTree](https://boards.straightdope.com/u/DemonTree)\ **Post date:** [August 30, 2025, 11:23pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/4 "2025-08-30T23:23:38Z")
What you need to know is the wet bulb temperature, the temp a thermometer shows if it’s dampened with water so evaporation cools it down. When the wet bulb temperature reaches 35°C (95°F), people die with hours. But recent research suggests even 31.5°C (88°F) could be deadly. There’s a wet bulb temp calculator [here](https://www.omnicalculator.com/physics/wet-bulb), which suggests 36.5°C (96°F) at 90% humidity would definitely be deadly, with a wet bulb temp of 35°C, and 33°C (91.4°F) would be potentially deadly, with a wet bulb temp of 31.6°C. These seem alarmingly low! ---
**Author:** ![DMC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dmc/32/18049_2.png) [@DMC](https://boards.straightdope.com/u/DMC)\ **Post date:** [August 30, 2025, 11:27pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/5 "2025-08-30T23:27:44Z")
Person to person. Activity to activity. Shade to full sun. ---
**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\ **Post date:** [August 30, 2025, 11:29pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/6 "2025-08-30T23:29:50Z")
Do we infer 90 degrees with 90% humidity isn’t that common? Anywhere? The question assumes no activity and no full sun. Just hot, humid air that you can’t escape. ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [August 30, 2025, 11:33pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/7 "2025-08-30T23:33:06Z")
It’s common in the tropics. People adjust by doing things early in the morning or late at night. Or not doing much work during the heat of the day. ---
**Author:** ![sunacres](https://avatars.discourse-cdn.com/v4/letter/s/4491bb/32.png) [@sunacres](https://boards.straightdope.com/u/sunacres)\ **Post date:** [August 30, 2025, 11:35pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/8 "2025-08-30T23:35:14Z")
In my experience humans are very adaptable. Where I worked on the Arabian Gulf, summer days were consistently above 125 degrees and very high humidity. I eventually learned to slow down and could operate a clipboard pretty much all day. But there were (other) imported laborers who would be in asbestos suits sandblasting the sides of oil storage tanks in the direct sun. All day. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [August 30, 2025, 11:35pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/9 "2025-08-30T23:35:15Z")
The wet-bulb temperature is the lowest temperature that can be reached at the current humidity by evaporating water - so if the combined humidity and temperature is high enough that the wet-bulb temperature is above 98.6 degrees or so, you won’t be able to cool off by sweating. That’s bad. > **[Wet-bulb temperature](https://en.wikipedia.org/wiki/Wet-bulb_temperature)** > > The wet-bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only. It is defined as the temperature of a parcel of air cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat supplied by the parcel. A wet-bulb thermometer indicates a temperature close to the true (thermodynamic) wet-bulb temperature. > More formally, the wet-bulb temperature is the temperature an air parcel would... ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [August 31, 2025, 1:21am UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/10 "2025-08-31T01:21:48Z")
> [@Andy\_L](#): > > The wet-bulb temperature is the lowest temperature that can be reached at the current humidity by evaporating water - so if the combined humidity and temperature is high enough that the wet-bulb temperature is above 98.6 degrees or so, you won’t be able to cool off by sweating. That’s bad. It is even worse than that; a wet bulb temperature at human core temperature is the maximum a health person can tolerate for more than a few hours but sustained wet temperatures even as low as 31 ºC as seen in tropic regions can make even that intolerable, and of course children, people with chronic health conditions, and the elderly who are less able to regulate body temperature may find even lower temperatures at near-saturation level humidity dangerous. > **[Humans can't endure temperatures and humidities as high as previously thought...](https://www.psu.edu/news/research/story/humans-cant-endure-temperatures-and-humidities-high-previously-thought)** > > Penn State researchers found that the maximum wet-bulb temperature humans can endure is lower than previously thought — about 31°C wet-bulb or 87°F at 100% humidity — even for young, healthy subjects. The temperature for older populations, who are... > _But in their new study, the researchers found that the actual maximum wet-bulb temperature is lower — about 31°C wet-bulb or 87°F at 100% humidity — even for young, healthy subjects. The temperature for older populations, who are more vulnerable to heat, is likely even lower._ Stranger ---
**Author:** ![penultima\_thule](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/penultima_thule/32/3833_2.png) [@penultima\_thule](https://boards.straightdope.com/u/penultima_thule)\ **Post date:** [August 31, 2025, 11:48am UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/11 "2025-08-31T11:48:23Z")
[![](https://i.ibb.co/6c2LFjKG/HSRI.jpg) ](https://i.ibb.co/6c2LFjKG/HSRI.jpg) ---
**Author:** ![penultima\_thule](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/penultima_thule/32/3833_2.png) [@penultima\_thule](https://boards.straightdope.com/u/penultima_thule)\ **Post date:** [August 31, 2025, 11:55am UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/12 "2025-08-31T11:55:06Z")
The NSW Cricket Association uses a heat index of temperature and humidity, plus allowances for windspeed to determine whether local weather conditions are too dangerous for play. If the index (available on an app) reaches 11 play is to cease immediately and players are to remain under shelter until the index has fallen below 10. The impact of humidity is exponential. And yes, play has been suspended periodically every season since it’s introduction. Previously the limit was based on reported temperatures at a local weather station (ie in shade) (42C) and yes I have been involved in games where that limit was breached. _(the graph above is of my creation, the app simply shows the index based on Bureau of Metrology data)_ ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 31, 2025, 6:03pm UTC](https://boards.straightdope.com/t/what-heat-humidity-combination-will-eventually-kill-you/1022617/13 "2025-08-31T18:03:40Z")
Here are my go to cites for these sorts of questions. They’re semi-redundant to other cites above, but more background is always good … - **[The emergence of heat and humidity too severe for human tolerance | Science Advances](https://www.science.org/doi/10.1126/sciadv.aaw1838)**. - **[Greatly enhanced risk to humans as a consequence of empirically determined lower moist heat stress tolerance | PNAS](https://www.pnas.org/doi/10.1073/pnas.2305427120)**