system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: I have endometriosis—how does my heating pad make my pain subside?
gpt
Heat or ice work for pain relief because effectively they offer two solutions.

Heat increases blood flow which promotes the ability of the body to heal. This is more useful for muscular pain such as those muscles in your pelvic area. This is more suitable for pain that is not caused by muscle tears or recent injury.

Conversely, Ice slows blood flow and is best to remove inflammation and slow the process. This is why you use ice on a sprained ankle so it helps reduce swelling. Technically ice could help reduce the swelling effects but it isn’t pleasant long term!

You should also consider the psychological effects of having something warm and comforting against you when you are in pain compared to something icy and cold. It’s the same reason we like physical comfort when we are sad or in physical pain.