There are a number of causes of dark circles around the eyes. It's hard to say for sure what the cause is in each case, but possibilities include:

Aging
The older we get, the looser the skin around the eyes tends to be. It becomes easier to see veins through the skin. Veins have a blue tinge to them. They may dilate when lying down or if you have nasal congestion or seasonal allergies. This causes the area around the eyes to appear darker than other skin.

Heredity
You are more likely to have dark circles around the eyes if your close relatives have them.

Fluid retention
Puffiness around the eyes may be more prominent after heavy salt intake, from pre-menstrual bloating or other causes of fluid retention, such as kidney or liver disease. Puffiness can contribute to loose skin that makes dark veins more noticeable, as noted above.

Besides makeup or other cosmetic approaches, there are a few things you can do about dark circles under the eyes. These include:

• Getting regular checkups and treatment for any condition that contributes to fluid retention
• Getting treatment for sinus congestion or allergies if you have these problems
• Limiting salt intake

Unfortunately, none of these is a reliable treatment, especially if you have a strong family history of dark circles under the eyes.