system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does ice reduce swelling?
gpt
Your body restricts blood flow to cold parts of your skin to conserve heat. When you dramatically cool down your skin with ice, your body reacts as if it's in a cold environment and constricts blood vessels flowing into that area as if to conserve heat.

Swelling is the result of blood vessels dilating to bring additional blood and resources to a part of you that has been damaged. The constriction to "conserve heat" counteracts the dilation in response to damage so overall less blood flows into the area and swelling is reduced.