system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does your face physically change (E.g. Get puffy or bags under the eyes) when you get little sleep?
gpt
This may be caused by the blood vessels under your eye. When you don't get enough rest, the blood vessels under your eyes can become dilated, bringing them closer to the surface and causing the area underneath the eyes to swell (causing puffy eyes) and/or appear purple, blue or even blackish in color (which causes dark circles).