system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why Does Cold Air Hold Less Moisture than Warm Air?

With the big drop in air temps in the northern US, I got to wondering about this.  I’ve read that people get itchy dry skin in the winter because cold air doesn’t hold as much moisture as warm air does. Assuming that’s true, what’s the reason for it?
gpt
The temperatures we like are very close to the temperatures where water condenses from a vapor (gas) to a liquid.  Colder temperatures, like the ones outside now, are below the temperature where water condenses and even below the temperature where it freezes.  When the water freezes, it falls out of the air.

When that air with no water is drawn into out homes and offices (so we have fresh air to breathe) we warm it up.  While warming it up would allow it to hold more water in the vapor state, that doesn't make water appear spontaneously in the air.  So we have warm, but very dry air, unless we have special machines that add water to the air as they warm it.