It is often claimed that periorbital dark circles are caused by tiredness or working too hard or even just staying up late. While this can be true, the truth is that your genes play a huge role here. So what exactly is happening when you get dark circles under or around your eyes?
Some people are more genetically inclined to develop dark circles. Dark circles occur because the skin under the eyes is quite thin and vulnerable to fluid compartmentalization. If the blood vessels in the region swell, the bluish color will show through as shadowy circles. 
When you are stressed more of your blood is directed to you main organs where your body needs it most rather than to your face which is left looking drained and a bit pastier. The contrast between the rest of your skin and the circles beneath your eyes can make the darkness appear more noticeable.
Cause: Unhealthy Habits
Excessive smoking and consumption of alcohol can lead to dark circles getting prominent. Excessive smoking makes your blood vessels appear more prominent, thus causing the dark circles. And of course, it is a no-brainer that smoking and consuming alcohol don’t do any wonders for your health. Also, try to avoid caffeinated drinks. 
Fatigue, seasonal allergies, sinus infections, high blood pressure and eating high sodium foods can all cause swelling and darkening of the area. Too much sun exposure can also be a cause as your skin produces more melanin, or skin pigment. Rough eye makeup removal, sleeping positions — especially face or side down — and eye rubbing can also cause dark circles to appear.
There are changes you can make that will reduce the appearance of dark circles under your eyes. Some are easy and others are a bit more challenging. However, the result will be that you’ll no longer look as tired and worn-out when you first get up in the morning.
 Information based on http://www.todayifoundout.com/index.php/2014/06/causes-dark-circles-eyes-sleeping-people-really-tired/
 Information based on http://www.hellomagazine.com/healthandbeauty/skincare-and-fragrances/2013052212698/dark-under-eye-circles-causes-treatement/
 Information based on http://www.stylecraze.com/articles/causes-of-dark-circles-you-should-be-aware-of/#gref