One of the biggest reasons people get bags under their eyes is because their parents have them. It's in your genes, and -- aside from plastic surgery -- there's not much that can be done about it. When you're young, lack of sleep, lack of exercise, a diet full of salty foods and water retention can also lead to bags. Sinus infections can cause them as well, by constantly stretching the skin beneath your eyes. If you notice that you have bags under your eyes early in the morning but they're generally gone by noon, it probably means they're being caused by fluid retention.