Sleep deprivation can lead to many things—memory lapses and weight gain among them. But you can thank your folks for the shadows under your eyes. "Dark undereye circles are the result of a concentration of veins beneath the very thin skin in that area," says David J. Leffell, MD, professor of dermatology at Yale School of Medicine. "They're determined by genetics and won't change with more or less sleep." Frequent late nights may cause fluid retention under your eyes, however, and that puffiness can draw attention to existing darkness there.