Varicose veins are enlarged and twisted veins that usually appear on the legs and thighs. They can be painful and cause discomfort, but they are generally not a serious medical condition. Varicose veins occur when the valves in the veins become weak or damaged, leading to the pooling of blood and enlargement of the veins.There are several factors that can contribute to the development of varicose veins, including genetics, age, gender (women are more likely to get varicose veins than men), pregnancy, obesity, and a sedentary lifestyle.