Dark circles are not really of much medical concern,these are just temporary and can be removed by treating the cause...
These are caused usually by dilated veins that drains from your eyes ,usually in the case of nasal congestions...or swelling of eyelids that appear as shadows below your eyes.
Another cause might be light carbon deposits that result from incomplete protein digestion. Incomplete protein digestion may result from insufficient hydrochloric acid in your stomach that may be caused from a lack of primarily B6 and Folic Acid.So taking adequate B6 and folic acid might help.
And it is believed that enadequate sleep also causes dark circles but the reason behind this is not so clear.Might be enadequate sleep reduces circulation thus creating shadows like apperances in eyes.
For treatment of dark circles you can try the following:
Apply skin creams that contain vitamin C or K, alpha hydroxy acid and kinetin.
Take a good sleep around 7-9 hrs but it varies from person to person.
Eat a healthy, balanced diet, take vitamins, and drink plenty of water.
Reduce intake of excessive salt and quit smoking if you smoke.These impair your circulation.
Dark circles can result from chronic skin conditions, such as atopic eczema. Dark circles can also run in families.Treatment for chronic and severe undereye circles is directed at the underlying cause, if known, and may include bleaching agents and laser therapy too.