Extrinsic External factors
Pressure Compression of tissue between bone and hard surface.
Shear Results from the application of a force parallel (tangential) to the surface of an object while the base of the object stays stationary. Shear stress causes or tends to cause two contiguous internal parts of the body to deform in the transverse plane (i.e. shear strain). (International Review, 2010; Young, 2017)
Friction The force that resists the relative motion of two objects that are touching. Frictional forces occur when there is continuous rubbing or sliding of a surface over the skin which results in a contact force that is parallel to skin. (International Review, 2010; Young, 2017)
Moisture Can be caused by incontinence, sweating, high temperature and wound exudate. The patient’s skin can adhere to the damp surface and exacerbate damage.
Intrinsic Factors within the patient
Malnutrition Caused by chronic disease, major surgery, nil by mouth status, neglect, poor social circumstances.
Immobility Sedation, anaesthesia, paralysis, pain, major trauma, chronic disease.
Age Lack of sensation, thinning of skin, underdevelopment in neonates.
Medical conditions Congested cardiac failure (CCF), chronic respiratory disease, diabetes, anaemia and neurological disease, vascular disease, poor perfusion.
Sensory impairment Reduced awareness of pressure - leading to reduced spontaneous movement.
Dehydration Slows down body’s metabolism, reduces skin turgor, makes skin more vulnerable to new wounds.

Other factors are also considered such as the following:

  • Previous pressure damage - scar tissue is avascular and therefore more prone to breakdown.
  • Psychological and social factors - acute depression leads to apathy and reduced movement.
  • Cognitive status - inability to recognise risk.
  • Blood status - poor vascular supply means that added pressure will lead to ulceration.

(Guy, 2012)