The most common cause is too much pigment in the eye area.
This is a natural part of the skin and is more common in people of Asian or African ancestry.The pigment shows through the skin under the eyes because it's so thin.
Blood vessels under the eye can show as a bluish black shadow and ageing skin can sag, throwing shadows under the eye, too much sun exposure can make the condition worse because it leads to skin wrinkles.
Always use a high factor sunscreen when you're going out in the sun, especially on the face and avoid going out in the heat of the day without a hat and sunglasses.
Often known as 'panda eyes', the condition can also be worsened by poor diet, too much alcohol consumption, smoking or even underlying medical conditions.
Allergic reactions, like hay fever, can cause skin around the eye area to darken over time, while nasal congestion can lead to swelling of the blood vessels that run from your eyes to your nose, which makes the skin darken. Constant rubbing of irritated eyes can also damage the skin, women who are pregnant may find that the skin around their eyes darkens due to hormonal changes and increased dilation of blood vessels, which are visible through the skin.