Dark under eye circles? You may be seeing those bad boys due to allergies, as nasal congestion can widen the blood vessels that drain from the area around your eyes, which causes them to darken. Sleep deprivation is usually the most common culprit, but oversleeping can also cause those babies to go to the dark side. And sometimes it’s just good old genetics that you drew the short straw on! I have dark circles under my eyes from lack of sleep, and I know how hard it can be cover them up—which is why I have always been so picky about my concealer!