It can be because you have coeliac disease, but you'd probably have other symptoms too
i'm not sure if it is, but an old friend of mine used to get dark circles n her doctor told her to take the iron supplements because she didnt have enuf iron in her blood. ask your doctor.
i got dark circles, it is genetic because i;ve got deep set eyes.
Cucumber I find doesn't really work, nor tea bags.. If i drink more water and get more sleep that helps but they are still always there.
I find hayfever and allergy reactions make my bags much worse in the summer. I just use Origins "No Puffery" Eye mask at night and in the morning, and No7 Concealer but I might try a YSL Touch Eclat one day.
I thought they were caused by a lack of sleep