Pressure sores are caused by pressure against the skin that
inhibits an adequate supply of blood to skin and underlying
tissues. Other factors related to limited mobility can make the
skin vulnerable to damage and contribute to the development of
pressure sores. There are three primary contributing factors:
• Sustained pressure. When your skin and the underlying tissues
are trapped between bone and a surface such as a wheelchair or
bed, the pressure may be greater than the pressure of the blood
flowing in the tiny vessels (capillaries) that deliver oxygen
and other nutrients to tissues. Deprived of these essential
nutrients, cells of the skin and other tissues are damaged and
may eventually die. This kind of pressure tends to happen in
areas that aren't well padded with muscle or fat and that lie
just over a bone, such as your spine, tailbone (coccyx),
shoulder blades, hips, heels and elbows.   • Friction. Friction
is the resistance to motion. When a person changes position or
is handled by care providers,