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It is often claimed that periorbital dark circles are caused by tiredness or working too hard or even just staying up late. While this can be true, the truth is that your genes play a huge role here. So what exactly is happening when you get dark circles under or around your eyes?
Simply put, periorbital dark circles are a result of the thin layer of skin below your eyes showing the blood vessels and the blood they contain more clearly than anywhere else on your body. (For reference, this skin around your eyelids, called periorbital skin, is on average about 0.5 mm thick compared to an average of about 2 mm thick on most of the rest of your body.)
Now, as you may or may not already know, the reason veins often look blue isn’t because the blood inside them is blue; it’s because your skin/subcutaneous tissue only lets blue/violet wavelengths of light pass through it. As a result, only blue light is reflected back and the veins look, well, bluish. (Veins often won’t appear blue if a person has darker or lighter skin. Rather, the veins tend to appear green or brown. On the other hand, people with extremely light skin, such as albinos, will typically have veins that show up as dark purple or dark red, more closely resembling the actual color of the blood running through the veins.)
It’s the exact same concept with the skin below your eyes. Those dark bluish circles are (usually) just the result of light being reflected back off of the blood vessels sitting just below the surface of that incredibly thin patch of skin. This is the same reason facial bruises are more prominent below or around the eyes; the thin skin just shows the blood from the ruptured blood vessels a little bit more clearly.
Again, as you may or may not know, as we age, our skin loses its elasticity and ability to regenerate and as a result, it becomes thinner. This is why more often than not, elderly people will have rather prominent periorbital dark circles regardless of how much they sleep. As with those who are genetically predisposed to having thinner skin below the eyes, it’s just biology.