Iron Deficiency

An iron deficiency (or anemia) can cause dark circles under the eyes, and can also make your skin look pale, which just accentuates the dark circles. A doctor can do a simple blood test to check for anemia.

Other Curable Causes

Iron deficiency is far from the only cause for dark circles, however. Other likely causes are allergies (including food allergies), dehydration, and any disease or illness that causes fluid retention.

Heredity and Age

Unfortunately, the problem tends to get worse with age, as collagen production slows and the skin under the eyes gets thinner, causing the underlying blood vessels to be more visible. Heredity also plays a major role--if either or both of your parents had dark circles, you're at a higher risk for them as well.

Watch Your Salt Intake

A diet too high in salt can also contribute to dark circles under the eyes, so try limiting your salt (and drinking more water) and see if the condition improves.

Traditional Chinese Medicine

Times UK reporter Jennifer Harper-Deacon, a registered naturopathic physician, says, "According to traditional Chinese medicine (TCM), dark circles under the eyes relate to kidneys and the adrenal glands, which are seen as the foundation of our vitality. Sufficient sleep is one of the simplest remedies to support these vital organs."

Source:

Remedies for Under-Eye Dark Circles

Times Online UK: Dark circles