Healthy veins consist of one-way valves that keep the blood flowing continuously in one direction towards the heart. If these valves fail or leak the blood will flow backwards increasing the pressure within the veins. Varicose veins are prominent veins that have lost their valve effectiveness, often times resulting veins that are dilated under pressure, elongated, rope-like, and thickened.
Spider veins are small-dilated veins located near the surface of the skin. They are visible red, blue or purple veins that resemble spider webs or tree branches on the thighs and lower legs. Spider veins can sometimes cover large areas of skin and cause discomfort, particularly after prolonged standing.