Varicose veins, congestive heart failure, and other conditions can cause swelling of the extremities, especially the feet and ankles. This swelling (edema) is caused when plasma (the fluid portion of blood) leaks out of the blood vessels and into the tissues.

The excess fluid in the tissues interferes with the blood's ability to feed the tissue cells and dispose of cellular waste products. The tissue becomes poorly nourished and fragile, resulting in stasis dermatitis. The disorder is common on the ankles because there is less supportive tissue in this area.

In stasis dermatitis, the skin becomes thin and inflamed, and open ulcers may form and heal slowly. The skin may darken. The skin, initially thin, may later thicken, perhaps because of itching and scratching of the area.