How does pressure ulcer develop?
A pressure ulcer is localized injury to the skin and/or underlying tissue usually over a bony prominence, as a result of pressure, or pressure in combination with shear
Anyone who stays in one place for a long time and who cannot change position without help is at risk of developing pressure sores. The ulcers can develop and progress rapidly, and they can be difficult to heal. Sustained pressure can cut off circulation to vulnerable parts of the body. Without an adequate supply of blood, body tissues can die.
There are many factors may cause pressure injury：
Also, the tolerance of soft tissue for pressure and shear may be affected by microclimate, nutrition, perfusion, co-morbidities and condition of the soft tissue.
Reference: Pressure ulcer prevention: pressure, shear, friction and microclimate in context. A consensus document. London: Wounds International (2010).