An ulcer is a sore on the skin or a mucous membrane, accompanied by the disintegration of tissue. Ulcers can result in complete loss of the epidermis and often portions of the dermis and even subcutaneous fat. An ulcer that appears on the skin is often visible as an inflamed tissue with an area of reddened skin. They can be caused due to a lack of mobility, which causes prolonged pressure on the tissues. This stress in the blood circulation is transformed to a skin ulcer. Ulcers often become infected, and pus forms.