system
Given the following post, respond as if you're commenting on Reddit:
human
Why does cold hurt?

I understand why hot hurts because it is actually damaging the skin, but what makes it so when I get in my car in the morning, the cold of the seat is cold enough to hurt?
gpt
Cold also is damaging to the skin. Frost*burn* and its nastier older brother frostbite are serious injuries. 

It's a funny quirk of water that it expands when it turns into ice (most other liquid's solid form is more dense than its liquid state). Have you ever tossed a beer or full bottle of water into the freezer and come back to a burst container? The container will crack, burst, or flat out shatter. The same thing happens to your cells if the water they contain freezes. Burst cells die. That's why the affected areas of frostbite look black - it's literally dead and rotting cells.

Your body doesn't want bits of it to die, so excessive cold pings those nocioceptors - the pain-sensing nerves - just as much as excessive hot does. It's even why cold can be described as burning. It's the same biological mechanism screaming "GET AWAY!" when it's too cold and too hot.