The start of necrosis typically looks like a localized area of tissue damage. It typically begins with an area of discoloration, often a mottled or splotchy appearance, and may be accompanied by swelling. As the tissue damage progresses, the area may take on a dark or purplish hue and may become firm to the touch. In some cases, blisters may form in the damaged area. In more severe cases, the affected area may become painful and may be accompanied by a fever. In extreme cases, the tissue may begin to die, resulting in an open wound. In these cases, the affected area may become soft, discolored, ulcerated, or even black. Necrosis can be caused by various factors, including trauma, infection, radiation, or a lack of blood supply to the affected area.