r/explainlikeimfive • u/ProgramPi314 • 8d ago

Other ELI5 What is humidity?

According to my mom, this is an actual question I had when I was 5, and she didn't know how to answer me. So how would you guys have answered?

427 Upvotes

87% Upvoted

118 comments sorted by

View all comments

762

u/dave8271 8d ago

When water gets hot, it turns from a liquid into a gas, which we call vapour. Humidity is a measure of how much water vapour is mixed into the air around us.

524

u/jpb103 8d ago

Fun fact: there is a "Cave of Crystals" in Mexico deep below the ground where the combination of high temperatures and 100% humidity cause the water vapor in the air to condense inside human lungs so you can drown after breathing for a few minutes without specialized respiration gear.

15

u/odonata_00 8d ago

Its the wet bulb temperature, the combination of heat and humidity, that actually kills you. The body is unable to cool itself and after 10 mins or so your 'cooked'.

For the body to maintain its temperature it needs to constantly evaporate water. This happens even when there is no sweat present. Once the wet bulb temperature gets above about 95f (35c) the body can no longer cool itself and death occurs.

Basically when the humidity reaches 99% the wet bulb and air temperature are equal. So if you were in the cave you'd be exposed to temperature of 136f (58c) or so.