Varicose veins are swollen and enlarged veins that usually occur on the legs and feet. They may be blue or dark purple, and are often lumpy, bulging or twisted in appearance.
Varicose veins develop when the small valves inside the veins stop working properly.
In a healthy vein, blood flows smoothly to the heart. The blood is prevented from flowing backwards by a series of tiny valves that open and close to let blood through.
If the valves weaken or are damaged, the blood can flow backwards and collect in the vein, eventually causing it to be swollen and enlarged (varicose).