What causes dark rings under your eyes?

In my oppinion it could be many different things but what stands out to me the most is this, My father works a night job. My father has been on his job for the last 17 years and he can't seem to get rid of the dark cicle around his eyes. What it comes down to is not getting enough sleepand just working hard Sinuses and/or allergies could also be the culprit. Sometimes it just runs in the family. I've worded night shift for the past two monts and have found that eyes have become darker. I already had dark circles around my eyes for many years. I'm getting the proper amount of sleep but I think the irregular sleep paterns take there toll. i get plenty sleep, dont work a graveyard shift & i have no family history yet i still get circles dark circles so i dont know the deal