What causes dark circles under the eyes, and what can you do about them?

Some people are born with a relatively deep hollow, or ''tear trough," in the corner of the eye near the nose, which can cast a shadow near the corner of the eye, said Dr. Sandy Tsao, a dermatologist at Massachusetts General Hospital. Other people, particularly those of Mediterranean descent, are born with dark pigmentation in the dermis layer of the skin, ''which creates a blue-black hue below the eyes."

Superficial blood vessels in the skin can also create ''a dark cast in some individuals all of the time, particularly if they have sinus problems or other problems which increase venous pressure in the area," said Dr. Bernard Cohen, a dermatologist at Johns Hopkins School of Medicine.

Dark circles, by the way, are different from saggy lower eye lids, or eye bags.

The circles often get worse when a person hasn't slept because of swelling around the eyes. Rubbing the eyes, as people with allergies often do, can also make things worse because this thickens and inflames the skin on eyelids.

Concealers containing green cover up the reddish hue from excess blood vessels, while yellow can cover dark pigmentation, said Tsao.

If the circles really bother you, you can try laser treatments. This usually involves both a Q-switched ruby laser to get rid of the dark pigmentation and a pulsed dye laser for the blood vessels. But, although it's safe, according to Tsao, it's not cheap -- about $1,500 for the three treatments -- and is not covered by insurance.

JUDY FOREMAN

E-mail health questions to Foreman@globe.com.