Bedsores are the result of pressure on the skin that reduces blood flow in and around the skin and surrounding tissues. Generally, doctors identify three primary causes of bedsores: 1) sustained pressure, 2) friction, and 3) sheer.
Sustained pressure happens when the skin and other tissues are trapped between a surface -- like a bed or wheelchair -- and bone. The issue relating to bedsores caused by sustained pressure relates to the restriction of blood flow in tiny blood vessels called capillaries which are essential to delivering oxygen and nutrients to the body tissues. When oxygen and nutrient flow is reduced, these tissues become damaged and begin to die. Areas of the body that are not well padded tend to be the most vulnerable to sustained pressure bedsores.
Friction bed sores happen when a patient's body and skin are dragged across a surface that resists its motion. If the skin is moist, a patient could be more at risk of developing a friction-related bed sore. The bruising and tissue damage hat results from this kind of injury can result in serious injuries that become seriously and/or fatally infected.
Shear-type injuries happen when the skin is pulled in two different directions. If the bones and tissues under the skin stay in place while the skin is pulled over the top, a pressure sore could develop.
Bed sores are serious injuries that need to be treated quickly before they develop into a potentially fatal injury. Bed sores are also preventable in most cases and if a patient develops one, it could be a sign that hospital or medical negligence has occurred.
Source: Mayo Clinic, "Diseases and Conditions Bedsores," accessed April 22, 2016