Vein conditions, such as varicose veins and spider veins, occur when veins become enlarged, swollen, or damaged. These conditions are commonly found in the legs and can be caused by weakened vein valves, poor circulation, or other underlying issues. Varicose veins are large, bulging veins that often appear dark purple or blue, while spider veins are smaller, red or blue veins that resemble a web-like pattern on the skin’s surface.