Why do I have dark circles under my eyes when I wake up?

Dear Dr. Cory:

Why do I have dark circles under my eyes when I wake up?

Melissa Pugh Abbyville, South Carolina

Dear Melissa:

The skin under the eyes is thinner than other areas of the body. Therefore the purplish color of the veins tends to show through more easily in this area. It is also believed that circles under the eyes can be due to not getting enough sleep. When you sleep, all of the functions of the body slow down. This increases the amount of oxygen in the blood. When you don't get enough sleep, the oxygen in the blood is slightly lower, causing the blood to become a darker colon This darker color shows through the thin skin under the eyes.

And finally, you might have what is called "allergic shiners." Certain allergies can cause blood to collect near the sinuses under the eyes and cause the darker color.