Are varicose veins caused by underlying health problems? Not necessarily. The only situation where you might be concerned that there is something else going on is if the varicose veins have clotted and you’ve got a lot of clot, or thrombophlebitis, in the superficial veins of the leg. That is sometimes due to the fact that you’ve got varicose veins, but it can be due to underlying health problems like extensive cancer. That is only the case in very few people, but it is just a little red light if you have extensive thrombosis all of a sudden: it needs investigating to check that you haven’t got anything more serious going on.