Varicose veins are formed because of weak vein walls you are genetically predisposed to it it is not steroid induced just hope you don't develop a varicose vein in your testicle (varicocele) now that you know you are predisposed to it be carefull.
There are more than one cause of them.... I know the more common is the weakness of valves in the vein which prevent the backward flow of blood away from the heart may cause poor circulation..
I have some too on the front of my calf near the shin. I think it is from Muy Thai kick boxing though. I think they are broken blood vessels that never healed correctly.