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Pressure sores are areas of damaged or broken skin. Sick people who sit or lie in one position for too long can get them quite quickly. Without treatment, they can become deep wounds that take a very long time to heal.

When you sit or lie down you naturally shift your position from time to time, even when you're asleep.

But if you can't move yourself because you are too ill or weak, or even unconscious, you could get a pressure sore.

Pressure sores are sometimes called pressure ulcers or bedsores.

Experts think pressure sores start when:^{1 2}

• The weight of your body presses down on the skin underneath. This pressure stops your blood from circulating properly through the skin, so the skin doesn't get enough oxygen or nutrients. If you don't shift your position, the skin cells die and the skin breaks down.
• The layers of your skin slide over each other as you slip down or are pulled up in bed. This is called shearing.
• Your skin is dragged across the mattress or seat as someone moves you. This is called friction.

Pressure, shearing and friction all damage your skin and increase the chance of a pressure sore. Areas of skin over the bony parts of your body are most at risk.^{2 3}

Anyone who has difficulty moving can get a pressure sore. But you are more likely to get one if you:^{2 4 5 6}

• Are very old or very young
• Are seriously ill, drowsy or unconscious
• Have had surgery
• Leak urine or feces
• Have a serious injury, such as a broken hip
• Are very overweight (obese)
• Don't eat or drink enough
• Have poor circulation, perhaps because you smoke
• Have had a pressure sore before
• Can't feel pain. This can happen if your spinal cord is injured, or if diabetes has damaged your nerves.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.