The cause of spider veins is unknown. They are so common that nearly everyone knows someone in the family who has had them. They are more prevalent in women but occur in men as well. They can appear locally after trauma or after superficial surgery, even after vein surgery. There is not much one can do to prevent them. The advice to avoid crossing the legs or wearing constricting clothing or garters to prevent them has no established basis. The hope that support stockings and dietary supplements are of help is unsubstantiated.