Why is humid air hotter

So when the relative humidity of the air is high, meaning the air has a high moisture content, the sweat evaporation process slows down. The result? It feels hotter to you. The opposite occurs if the air is very dry. Even on a degree day, it can feel a little cooler to the body if the air is dry because sweat evaporates quickly.

Want to calculate the heat index on your own? That's because humidity — the amount of water vapor moisture air possesses — can make it difficult to shed excess body heat through sweat, according to the National Oceanic and Atmospheric Administration's NOAA's National Weather Service. Ordinarily, as sweat beads onto the surface of our skin, heat from our bodies evaporates that sweat into the air, thereby cooling our skin.

Humidity, however, prevents sweat from evaporating as readily, because the surrounding air already has a high moisture content and can't absorb much more. And the less that moisture evaporates from our skin, the more uncomfortably warm we feel. Related: Why does being in the heat make us feel tired? High temperatures enhance humidity's ability to thwart temperature regulation, because warm air can hold more moisture than cool air can.

This explains why humidity feels more uncomfortable in summer than in winter , even if the humidity levels happen to be identical. Not only is hot and humid air stuffy and sticky on the skin, it's also a chore to breathe. But its "heaviness" isn't due to its high water vapor content, according to The Washington Post's Capital Weather Gang. Pseudonyms will no longer be permitted.

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