system
Given the following post, respond as if you're commenting on Reddit:
human
Why do people's faces turn red when they're embarrassed?

Exactly as the title says.  The body's natural reaction to embarrassment is to flush with blood and turn red.  What mechanism or survival instinct causes this and why?
gpt
Any sort of stress increases adrenaline production in the body.  Adrenaline opens up your blood vessels, allowing you to be temporarily faster or stronger, which is usually helpful in the face of a threat.  You have a lot of blood vessels in your face near the surface that open up causing your face to get red.