Bags under the eyes are caused by fluid retention due to lymphatic changes or age-related fat herniation.

“generally the bags are caused by two things one fluid retention so there's some lymphatic change that occurs under the eyes that's most noticeable because the skin under our eyes and on the surface of our eyelids is the thinnest so fluid changes are seen the quickest there and as we're in a supine or prone position fluid moves from our extremities back to our Central ner Venus system and it's easier to collect in the face so we see it around the face the other thing that we do notice with bags is just age related fat herniation that shows up more um as we wake up because of positional changes”