Spider veins are tiny, superficial, red or purplish veins that usually appear on the legs, or sometimes the face. They generally assume one of three patterns: spider-shaped, with many veins radiating from a central spot; linear, with small, unconnected lines; or arborizing (AR-bohr-eye-zing), in which a branch-like pattern is seen. Spider veins become visible due to excess blood pressure that dilates the vessels. However, doctors aren't sure exactly why this happens. One major theory is that they arise from deeper varicose veins which elevate pressure in tiny vessels near the surface. Another explanation is that spider veins have accidentally connected themselves to much higher pressure arteries, causing the veins to swell under the unusual tension. Whatever their cause, certain factors can encourage spider veins to develop, including pregnancy, jobs that require constant standing, birth control pills or hormonal changes, and being overweight. A tendency toward spider veins may also be inherited. There is little that can be done to prevent this cosmetic problem, but some practices may limit the number of veins that are formed. It may help to maintain a normal weight, exercise regularly, avoid prolonged sitting or standing, and elevate your legs at the end of the day.