Periorbital dark circles (also dark circles or raccoon attack) are dark blemishes around the eyes. There are many causes of this symptom, including heredity and bruising.
Causes
Heredity
In most cases, the dark circles under the eyes are blood vessels that can be seen through the skin. The skin around the eyelids (periorbital skin) is the thinnest skin in the body (around 0.5 mm thick compared with 2 mm in other areas). Like varicose veins, dark circles under the eyes are usually an inherited trait.
When blood passes through the large veins close to the surface of the skin, it can produce a bluish tint. The more transparent the skin--also an inherited trait--the darker the circles appear. In people with a deep-set bone structure, shadowing can also contribute to the dark color under the eyes.
Allergies, asthma, and eczema
Any condition that causes the eyes to itch can contribute to darker circles due to rubbing or scratching the skin around them. Hay fever sufferers in particular will notice under-eye "smudges" during the height of the allergy season. Some food allergies can also cause the area under the eyes to appear darker.