Dark circles under the eyes are a common skin condition where the skin under the eyes is darker than the surrounding skin. It can have a variety of causes, including genetics, age, stress, fatigue, allergies, smoking, dehydration, and overexposure to the sun.

The skin under the eyes is thinner and more sensitive than the rest of the face, and this can lead to visible blood vessels and discoloration. If the skin under the eyes swells, it can emphasize the dark circles even more.