The skin underneath the eyes is so thin and delicate that when blood vessels there are engorged, dark circles appear. As you age, the under-eye skin thins even more -- making dark circles more prevalent. Genetics, allergies and poor beauty habits all contribute to dark circles. If they appear suddenly, it may be an indication of seasonal allergies, a sinus infection or injury to the area. If the dark circles are accompanied by swelling and pain or isolated to one side, consult your doctor.
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Dark Circle Reasons
Dark circles occur because the skin under the eyes is quite thin and vulnerable to fluid compartmentalization. If the blood vessels in the region swell, the bluish color will show through as shadowy circles. Fatigue, seasonal allergies, sinus infections, high blood pressure and eating high sodium foods can all cause swelling and darkening of the area. Some people are more genetically inclined to develop dark circles. Too much sun exposure can also be a cause as your skin produces more melanin, or skin pigment. Rough eye makeup removal, sleeping positions -- especially face or side down -- and eye rubbing can also cause dark circles to appear.