How long does it take for pressure ulcers to form?

Duration for PUs. 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.