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Carpal tunnel syndrome is caused by pressure on a nerve in your wrist. It is a painful condition. At first, your hand may start to tingle or feel numb at night. You might find you drop things as your grip becomes weaker.

Your carpal tunnel is a narrow gap running through the bones and ligaments in your wrist. A nerve that gives you feeling in your hand (the median nerve) passes through this tunnel. So do the tendons (cords of tissue) that bend your fingers and wrist.

Your carpal tunnel is quite narrow and rigid. It's easy for the nerve inside the tunnel to get squeezed. This interferes with the messages that the nerve is sending to your brain. You might feel unusual sensations of numbness, tingling, burning or pain in your thumb, fingers and palm of your hand.¹ Your symptoms could be worse at night or when you wake up (many people sleep with their wrist bent and pressing on the nerve).²

It's not easy to say exactly what causes carpal tunnel syndrome.³ But certain things make you more likely to get it. These things are called risk factors. They include:^{3 4}

• Having had a small carpal tunnel since you were born
• Getting an injury to your wrist that causes swelling, such as a fracture or sprain
• Regularly doing things that put a lot of pressure on the wrist and where you repeat a movement. There are many activities like this. Examples include using power tools, cleaning, sewing and working on an assembly line
• Having fluid retention (your body holds onto extra fluid) during pregnancy or menopause
• Having a cyst (a swelling full of fluid) or tumor (a growth) in your carpal tunnel
• Having certain medical conditions, such as diabetes or rheumatoid arthritis ¹
• Being overweight (or losing weight quickly) may cause swelling around the median nerve.

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.