What are other causes of dark appearance under eyes?

Question

Besides general genetic trait or lack of sleep or vitamin deficiency, what are other causes of random dark circles under eye. I have a friend she gets them randomly out of no where and then they seem to disappear within an hour or so. It happens frequently. Is there some sort of disease she may have?

Answer 1

If it disappears within an hour I think she may have been rubbing her eyes.

Tell her to eat citrus fruits for healthy blood vessels.

Answer 2

she probably doesn't get enough sleep.