An ulcer is a break in the upper layer of the skin called the epidermis. This provides an entry way for bacteria and other infectious agents into the other layers of tissues below. Ulcers can form in any part of your body where the blood supply is poor and for most people, leg ulcers occur mainly in the lower limb or calf. In most people minor breaks in the skin will heal up without difficulty within a week or two. However, when there is an underlying problem the skin does not heal and the area of breakdown can increase in size. This is a chronic leg ulcer.