Varicose veins are commonly enlarged, distorted superficial veins that are a result of a weakened vein wall or damaged valves and have consequently lost the capacity to efficiently return blood to the heart. Varicose veins are found at the surface of the skin and have a raised, lumpy, dark-bluish appearance. Often confused with spider veins, varicose veins are different in appearance from spider veins, but their causes may be similar.

In order to understand how varicose veins occur, and can be treated, it is helpful to know about the three types of veins.