Occurrence of under-eye dark circles is due to an array of reasons and becomes obvious with aging. Thinning and wrinkling of the fine nature of skin under eyes occurs due to being exposed to ravages of nature. Thus any minor or major fluctuations in overall health are instantaneously reflected on the eye and adjoining area. It is often believed that tiredness or being exposed to sun causes dark circles, but it is not characteristically true in many cases. Often hormonal fluctuations could be contributory to what causes dark circles under the eyes. At times, under-eye dark circles are the result of darkness or shadowy effect cast due to puffiness in lower eyelid (innate fat bulges) that develops under eyes as one ages.
What causes dark circles under the eyes?
There are several causative factors leading to what causes dark circles under the eyes.
- Age
Ageing-related thinning and lost suppleness occurs in skin that covers eyelids due to which underlying blood vessels become more visible. Several physicians advice intake of vitamin C or ascorbic acid supplements to promote collagen production and revitalizing delicate skin in the eye area. 
Genetics
Predisposition to allergy or thin eyelids is often heritable and tends to runs in families.- Presence of Allergy
Though presence of allergies is mostly accountable for dark circles, any aspect which is causative to acute nasal blockages could be the offender. Even slight nasal stuffiness or swelling in eyes could be contributory and even a major allergic reaction like gasping, sneezes or chest congestion might not necessarily have to be present to cause dark circles. A basic skin, blood or other testing methods are available that help in pinpointing actual cause being either environment or food related. - Weariness or dearth of sleep
Fatigue could augment already existent or be causal to dark circles. Eyes are immensely strained due to protracted periods of glaring a computer screen or inadequate sleep. - Smoking
Second-hand smoke could be equally contributory as those who engage in smoking. Majority of the individuals could suffer vicious reactions on exposure to smoke like reddishness in eyes or becoming excessively teary whereas there could be others who develop swelling in eyes. Smoking has been found to obliterate significant levels of vitamin C on every occasion a cigarette is lit. - Excessive sodium intake
Those people who consume excess amounts of salt in their day-to-day food intake could also be one of the causal factors to dark circles as it may augment water retention in body. An ideal approach is trying and restricting consumption of raw salt in foods. - Fluid retention
Fluid retention could be a significant reason for swelling in eyes. It is advisable to take daily vitamin C intake as it is an innate diuretic (substance which has a tendency of increasing urination), however it could additionally help in collagen production. - Other reasons
Several other aspects could play a role like menstrual cycles, gestational period, thyroid conditions and being overly exposed to harmful ultraviolet rays of the sun.
