Valves inside the veins keep the blood moving back toward the heart. These valves prevent the force of gravity from pulling blood back down toward the feet.
When the veins are damaged, gravity will hinder normal blood flow causing blood to form pools in the weakened, damaged veins. The pooling blood causes these veins to enlarge. Twisted masses of veins beneath the surface of the skin, know as varicose veins, often result. Varicose veins are larger and located deeper in the leg than spider veins. Spider veins are small, blue and purple veins on the surface near the skin.
Wearing a 15-20 mmHg* compression stocking can help prevent varicose veins from forming!