Sun exposure: As you might have already known, increased exposure to Sun spells danger for the skin. Pigmentation of the skin can produce dark circles while an excess of melanin production can make the dark circles appear darker. If you often step out under the scorching sun, make sure to wear a sunscreen with adequate SPF before moisturizing.
Sleep deprivation: While sleep deprivation can compound the problem by making the skin paler, you might be surprised to find that it is not often the major cause of the bothersome development. There are a lot of other things that can contribute to the paling of the skin, fatigue resulting from stress and illness, to name a few.