Home > What causes an ulcer on the leg? > What causes an ulcer on the leg? What causes an ulcer on the leg? Home > What causes an ulcer on the leg? > What causes an ulcer on the leg? Venous leg ulcers are caused as a result of the skin breaking down, usually due to severe varicose veins. It can take many years to develop an ulcer and they are more common in the elderly due to more inactivity, however they can affect anyone at any age.