There are many contributing factors to dark circles, these include:
GENETICS - family history plays a huge part into whether you have or will develop dark circles.
LACK OF SLEEP - this can cause your skin to become dull and pale, which will allow the dark tissues and blood vessels beneath your skin to show.
AGE - the natural ageing process is another common cause. As you age, your skin becomes thinner. As this occurs, the dark blood vessels beneath your skin become more visible causing the area below your eyes to darken.
DEHYDRATION - this is a common cause of dark circles under your eyes. When your body is not receiving the correct amount of water intake, the skin beneath your eyes begins to look dull and your eyes look sunken.
EYE STRAIN - staring at your television, phones, tablets and computer screens can cause significant strain on your eyes. This strain can cause blood vessels around your eyes to enlarge. As a result, the skin surrounding your eyes can darken.
ALLERGIES - allergies and eye dryness can trigger dark circles. When you have an allergic reaction, your body release histamines as a response to harmful bacteria, the histamines also cause your blood vessels to dilate and become more visible beneath your skin.
Also, allergies increase your urge to rub and scratch the itchy skin around your eyes, this can then worsen your symptoms, causing inflammation, swelling, and broken blood vessels, which can result in dark shadows under your eyes.
SUN OVEREXPOSURE - overexposure to the sun can cause your body to produce an excess of melanin(pigment), causing pigmentation in the surrounding skin to darken.