system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why is hot good for some inflammations, but for others it's better cold?

For example, if I have an inflammation in my arm resulting from bumping into something, or someone kicked my balls, I would use an ice pack. But if a woman is on her period (since the uterus swells), or I have a swollen throat, it's better for the woman to use a heat pack, or for me to drink something warm or hot. Why is that? Aren't inflammations basically areas of the body with enlarged blood vessels or filled with liquid? What's the difference between inflammations that require hot or cold?
gpt
Heat opens blood vessels, bringing more oxygen and nutrients to an area. Cold shrinks blood vessels, it is used to reduce swelling and inflammation of an acute injury. For situations where muscle spasm is part of the problem like a back sprain or uterine cramps, heat relaxes muscles, helping to reduce the pain.