Estrogen in hormone replacement therapy and contraceptives can aggravate eyelid pigmentation. Aging - with age, the eyelid skin thins and the fat pad below the eye shrinks producing a sunken look to the eyes. Bruising of the eyelids i.e. trauma, surgery or repeated minor injuries. Broken capillaries of the eyelids. Eye architecture - deep set eyes cast an optical illusion of darkness around the eyes.
Some people also inherit thinner eyelid skin which increases melanin and blood vessel visibility.
Also stress, poor behavioural lifestyle and improper nutrition may enhance dark eye circles.