Most Helpful Girl
Dark circles under your eyes are from burst capillaries (its like a bruise under your eye) and they occur from lack of sleep, stress, and even hereditary issues.
Using a cool rag will help slightly, but one of my moms tricks is to use preperation H. It calms the inflammation.
As far as the concealer and foundation comment by the other girl- make sure you put them on in this orcer:
It is important to put concealer on AFTER foundation to create a more even-less cakey look. The less makeup the better because makeup tends to intensify the shadows under your eyes if the "begs" are sunkin in or sticking out.
I got the makeup tip from a few different magazines and a makeover show. I do it myself because I get dark circles (love the insomnia) and it works pretty well.
There are also color correctors out there. If the circles are a reddish tint, you apply the green corrector before concealer and if they are more blueish, you use the yellow.