Unrelieved pressure: Skin and underlying tissues are

compressed between bone and another hard surface e.g. bed,

trolley, chair. Disruption to the microcirculation causes tissue

hypoxia and tissue breakdown.

Shearing forces: Poor lifting or repeated slipping down the

bed, causes distortion of the microcirculation and severing of

tiny blood vessels leading to tissue breakdown.

Friction: Repeated rubbing of bony areas e.g., elbows causes

superficial abrasions.