Why is 100 degree weather with high humidity so much harder to take than 100 degree weather when the humidity is very low? Why does moisture in the air exacerbate discomfort during the summer heat?

It absorbs the heat in the air and since the air is saturated your body cannot dissipate the heat as quickly compared to dry air that would absorb the sweat and heat.

It´s twice as uncomfortable.

It makes for a very miserable season.

I hate hot , muggy weather.  Hate it.

I don't know but the heat and humidity is slowly driving me to my grave.

it probably makes people feel it more, heat dont seem to bother me any

Because the human body relies on the cooling effect of sweat evaporating.. In low humidity the rate of evaporation of sweat off your skin increases.. Dry air evaporates water quickly..  In air that is already laden with water ..Humid air... the amount of water that air can evaporate off you skin is much lower.. therefore the cooling effect of humid air is much lower the dry air..

I was going to explain it, but you seem to have done so adequately (and probably in less space than I would have consumed...;-D...)

Thank you for your helpful reply Adam. I appreciate it. Happy Tuesday! :)

Mahalo for your reply OS and Happy Tuesday! :)

 Thank you for your reply HarryD! :)

Me too. Southern California thankfully is hot/DRY. I've been in hot/MOIST and you need a zillion showers during the day. I guess you can adjust to anything if you have to do so. Thank you for your reply Uc! :)

I hope not. Don't know where you live Semper Fi but southern  California is hot/DRY! It's bearable. Thank you for your reply and Happy Tuesday!  :)

What about humidity pearl? Does that bother you at all? Thank you for your reply! :)