How do pressure ulcers form?

Multifactorial: Pressure ulcers are rare, though possible in the young - as in a 10 hour back surgery. It is more common in the elderly / infirmed with issues like stroke related paralysis/paresis, cachexia, metabolic problems like diabetes and chronic illness like kidney disease. Add prolonged pressure to the above, even healthy looking tissue will breakdown and not heal properly.

Dr Ali and another doctor agreed

Pressure: Normally if you sit or lie on the same area for too long it will begin to hurt and you shift your weight. If you cannot feel because of illness or if you are in one position and can't move you may develop a pressure injury.

Dr Sparacino agreed

Causes of Pu: Pressure ulcers are due to 'enough' pressure to occlude the blood pressure of the microscopic capillaries. No one is sure how long it you must occlude these capillaries so that a pressure injury results in changes in the skin. It will vary from person to person because of multiple factors in addition to time: repeated episodes, moisture, nutrition, protein stores, ability to heal, diabetes mellitu.

Cuts off blood: At the most basic level pressure cuts off local blood flow until cell death or irreversible injury to cells occur numerous host factors affect this as well including nutrition, diabetes, baseline local blood flow, sensory loss paralysis etc all aggravate the situation.