With my extremely limited knowledge of thermodynamics, it seems like high humidity would provide enough water to transfer some of the summer heat.
Is it enough to make a difference?
Prompted by my [r/unpopularopinion post](https://www.reddit.com/r/unpopularopinion/comments/ic8rd8/humid_heat_is_better_than_dry_heat/?utm_source=share&utm_medium=ios_app&utm_name=iossmf)
Thanks so much for your responses! I had no idea that cooling came from the evaporation of sweat versus the just having water on you. I was going to reply to everyone, but the response seems to be the same across the board. I really appreciated everyone taking the time to educate little ole me 🙂
In: Physics
Humidity is probably considered the more dangerous one overall. I for one know my asthmatic lungs like humid air far better than dry air
High humidity blocks your body’s ability to effectively shed heat. We produce sweat to help us cool effectively, and when sweat gets evaporated by the environment, it cools us. When there’s a lot of water in the air already (humidity), sweat doesn’t get evaporated as well.
This is also why there are significant heat illness/stroke issues in the southeast. Additionally, elderly have a decreased ability due to age to effectively cool themselves, placing them at higher risk for those issues as well.
High humidity prevents you from cooling due to your sweat evaporating, so high humidity is much more dangerous. For instance at 100% humidity, your sweat wouldn’t evaporate at all.
It’s not the presence of moisture that cools, it’s the act of evaporation. Sweat has cooling power because [water soaks up heat energy when it changes from liquid to gas](https://en.wikipedia.org/wiki/Enthalpy_of_vaporization). But at a given temperature, air can only hold so much water vapor. The more humid it is, the harder it is for water to evaporate, and sweating becomes less effective.
Dry heat is dangerous not because it’s harder to cool off, but because it’s easy to become dehydrated. Since sweat evaporates instantly in a dry heat, we *feel* cool and don’t seek water.
It’s far easier to cool off in a dry heat.
I live in the tropics and have worked in 45c heat both dry and humid. Give me dry 45c vs 30c humid any day
I once spent a few days above a wet-bulb temperature of 32C.
With 100% humidity and 32C your body is unable to shed heat and after a few hours of activity in this weather even healthy heat adapted athletes will begin to die.
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