There are two changes to the skin’s structure that are responsible for dark circles.
Firstly, the infraorbital fat pad, which sits directly under the eye, becomes thinner as we age. The fat pad has an underlying collagen (yellow) colour, but as it diminishes, the area appears darker. This dark shading is in fact the muscle under the eye, which becomes more visible as the infraorbital fat pad decreases.
Secondly, if the microscopic blood vessel structures are damaged, the body attempts to repair the damage by proliferating many small new veins, which further darkens (reddens) this area. Sinus and nasal congestion can also contribute to increased blood flow in this area. The vessels become congested also, which is seen visibly as darkening.
Serums containing Vitamin C and Vitamin A can help to strengthen the collagen layer, by stimulating the skin to produce more collagen. Evidence suggests that Vitamin A (retinaldehyde) is also useful in strengthening new blood vessel structures.
Dermal Fillers can sometimes be used to supplement the infraorbital fat pad and reduce the appearance of dark circles.
In severe cases, a surgical procedure called Blepharoplasty may be recommended. This procedure removes excess fat from beneath the eye, eliminating the ‘bag’ effect. The result is that the overlying skin appears firmer and smoother.