Stage one ulcers show superficial reddening of the skin that does not whiten when pressed. If diagnosed and treated immediately, a stage one bedsore usually heals within three or four days.
Stage two pressure ulcers involve superficial lesions of the skin resembling an abrasion or popped blister. With appropriate treatment such wounds may heal in four days to three weeks.
Stage three ulcers go deeper, forming an open crater-like sore, but muscle or bone are not exposed. The main risk is infection and serious complications, including an infection entering the bloodstream. With sustained treatment healing may take up to four months, depending on the depth of the sore.
Stage four pressure ulcers expose muscle and bone and are very difficult to treat. Tendons, nerves, and joints may be damaged, and the condition is potentially life-threatening.