system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does applying more heat help with inflammation? (Eg heat packs, hot water bottles)
gpt
Inflammation is characterised by 5 signs - redness, swelling, pain, high local temperature and dysfunction. Big part responsible for these is the "pooling" of blood at the inflamatory site. Because of the high pressure of the blood inside capillaries it is forced outside their walls and into the surrounding tissue. 
 Now, for the first 24 hours it is wrong apllying heat, you should instead apply cold compresses, because heat expands the capillaries and makes it easier for thinga to get out. If 24 hours have passed, and enough outside liquid is pooled, it exercises pressure on the blood vessels and shrinks them, that's when heat can help get them expanded, so they can start collecting that external liquid.