Bags under eyes — mild swelling or puffiness under the eyes — are common as you age. With aging, the tissues around your eyes, including some of the muscles supporting your eyelids, weaken.
Oversleeping, extreme fatigue, or just staying up a few hours past your normal bedtime can cause dark circles to form under your eyes. … Lack of sleep can also cause fluid to build underneath your eyes, causing them to appear puffy. As a result, the dark circles you see may actually be shadows cast by your puffy eyelids.