How Pressure Injuries Form

Even a healthy person can begin to develop pressure injuries in less than a day if left in the same position. It helps to know where and how pressure injuries develop and what you can do to prevent them.

Healthy skin has a subcutaneous layer that contains blood vessels and cushioning fat. The dermis is where new cells are made. Bones support the body. Sweat glands lubricate the skin. The epidermis is the outer protective covering. Surface pressure is balaned by body weight pressure. In fragile skin, the subcutaneous layer has fewer and flatter fat cells. Bones protrude. Fewer sweat glands make less lubrication. The epidermis is dry and loses cell layers. The dermis produces cells more slowly. Surface pressure can result in sores.

Unrelieved pressure

People who can’t move for long periods of time are at risk for pressure injuries because oxygen and other nutrients can’t easily reach their cells. An immobile person with skin made fragile by age or disease is at even greater risk. This skin heals more slowly. Some persons have decreased sensation in these areas and don't feel the painful ulcerations developing.

Shear and friction

Two forces contribute to pressure injuries. Opposite, but parallel, sliding motions—like bone moving down and skin up—compress blood vessels. Surfaces rubbing (friction) can also cause skin to break down.

Put your finger on your shin and press down hard. Slide your finger up and down, allowing it to move roughly over your skin. As the skin slides over the bone it pulls and stretches. This is called shearing. If you continue sliding your finger up and down with enough pressure in both directions it can cause the skin to tear. This is especially true in an older or sick person whose skin isn't as tough as it used to be.


Moisture buildup

Skin overfilled with fluid is fragile. And certain kinds of fluid—sweat, urine, or feces—can provide a source for bacteria growth, delaying healing. Too much moisture carries another risk: it can increase friction.

Poor nutrition

Cells repair damage slowly if they do not get enough nutrition. This is especially true for a person who is sick or has an injury to the skin. When a person loses a lot of weight from not eating well and having poor nutrition, it makes the skin very thin and very weak and fragile.