Leg veins form as a result of heredity, hormones (especially pregnancy), and poor circulation (prolonged standing or leg crossing). Spider veins can be treated safely and effectively with sclerotherapy—which involves injection of a concentrated saline solution into the veins. Typically, one to three treatments are necessary to remove most of the veins. Besides mild and temporary bruising, side effects are unusual. Finer veins can be subsequently treated with a laser.