Carpal tunnel syndrome happens when the median nerve gets squeezed as it passes through a narrow passageway in your wrist. This passageway, the carpal tunnel, is bordered by wrist bones on three sides and a tough ligament across the top. Anything that shrinks that space or increases pressure inside it can compress the nerve and trigger symptoms like numbness, tingling, and weakness in your hand.
How the Nerve Gets Compressed
The carpal tunnel is surprisingly tight. Nine tendons and the median nerve all share this small channel, and normal pressure inside it ranges from just 2 to 10 mmHg. That pressure is sensitive to wrist position: extending your wrist (bending it back) increases pressure roughly tenfold, and flexing it forward increases pressure about eightfold. This is why you might notice symptoms flare when you sleep with bent wrists or hold a phone for a long time.
When pressure stays elevated, blood flow to the nerve slows down. The tiny blood vessels running alongside the median nerve can’t deliver enough oxygen, and the protective barrier around the nerve starts to break down. This leads to swelling inside the nerve itself, which takes up even more space in the tunnel and creates a cycle of worsening compression. Over time, the nerve’s insulating sheath can be damaged, slowing the electrical signals that control sensation and movement in your thumb, index, middle, and ring fingers.
There are two specific pinch points where compression tends to happen: at the entrance of the tunnel, where the wrist ligament begins, and at the narrowest section near a small hook-shaped bone called the hamate.
Repetitive Motion and Workplace Risks
Repetitive hand and wrist movements are among the most widely recognized triggers. Jobs that involve gripping, pinching, or flexing the wrist for hours create repeated spikes in tunnel pressure. Assembly line work, meat packing, and construction are classic examples, but office work contributes too. Typing on a conventional keyboard produces measurably higher carpal tunnel pressure than simply holding your hands in the same position, and the effect gets worse as your wrists angle further back. At 45 degrees of extension, pressure during typing nearly doubles compared to a neutral wrist position.
Vibrating tools are another occupational hazard. Prolonged use of grinders, jackhammers, and similar equipment causes cumulative trauma to the hands and wrists. Gripping a vibrating tool tightly amplifies the force transmitted into your hand, and tools with uneven wear or poor alignment make the problem worse. Cold, wet conditions compound the effect because they reduce blood flow to the hands. Occupational health guidelines recommend 10-minute breaks for every hour of continuous vibration exposure, lighter grip pressure, and keeping hands warm and dry.
Body Weight and Fat Accumulation
Higher body mass index is a well-established risk factor. The leading theory is straightforward: excess fat can accumulate inside the carpal canal itself, physically narrowing the space available for the nerve. This added pressure reduces blood flow to the nerve and can damage its protective insulation. Large genetic studies confirm that BMI is not just correlated with carpal tunnel syndrome but appears to be causally linked through shared biology. Losing weight won’t guarantee relief, but it can reduce one source of pressure on the nerve.
Pregnancy and Hormonal Changes
Carpal tunnel syndrome is common during pregnancy, with reported rates ranging widely from under 1% to as high as 70% depending on how strictly it’s diagnosed. The mechanism is fluid retention. As blood volume expands during pregnancy, tissues throughout the body swell, including the lining of the carpal tunnel. That swelling raises pressure inside the tunnel and compresses the median nerve. Symptoms typically appear in the second or third trimester and often resolve within weeks to months after delivery.
Hormonal shifts outside of pregnancy can play a role too. Early use of hormone replacement therapy shows a genetic correlation with carpal tunnel risk, suggesting that fluctuations in estrogen and progesterone may influence fluid balance and tissue swelling in the wrist.
Inflammatory and Metabolic Conditions
Several chronic diseases make carpal tunnel syndrome significantly more likely by changing the tissues inside the tunnel.
- Rheumatoid arthritis causes the joint lining in the wrist to expand aggressively, forming invasive tissue called pannus that physically invades the tunnel space. The combination of joint erosion, loosened ligaments, and inflamed tissue raises carpal tunnel pressure and chokes off blood supply to the nerve.
- Psoriatic arthritis drives increased inflammation and new blood vessel growth in the wrist’s joint lining, which narrows the tunnel from the inside.
- Diabetes makes nerves more vulnerable to compression. Elevated blood sugar damages small blood vessels throughout the body, including those feeding the median nerve, so even modest pressure increases can cause symptoms.
- Thyroid disorders (particularly hypothyroidism) can cause tissue swelling that crowds the tunnel, similar to the mechanism in pregnancy.
- Scleroderma stiffens the median nerve itself, making it less able to glide smoothly through the tunnel and more susceptible to mechanical stress.
Tissue samples from people with rheumatoid arthritis or lupus who develop carpal tunnel show markedly higher levels of connective tissue growth factor compared to people who develop it without an underlying disease. This suggests the inflammatory process actively remodels the tunnel lining, making it thicker and less compliant.
Genetics and Wrist Anatomy
Some people are born with a narrower carpal tunnel, and that alone raises their baseline risk. A large genome-wide study published in Nature Communications identified 50 genetic locations linked to carpal tunnel syndrome. Many of these genes control the production of collagen, the structural protein that forms the scaffolding of bones, cartilage, and ligaments. Three key genes (COL11A1, COL11A2, and COL10A1) encode collagens critical to bone and cartilage structure. Variations in these genes can alter the thickness of cartilage and the composition of the tissue matrix in and around the wrist.
Height also shows a genetic correlation with carpal tunnel risk, likely because skeletal proportions influence the dimensions of the tunnel. If carpal tunnel syndrome runs in your family, it may reflect inherited differences in wrist bone structure or in the composition of the ligament that forms the tunnel’s roof, not just shared habits or occupations.
Wrist Position and Everyday Habits
Even without a repetitive job, the way you position your wrists during daily activities matters. Research measuring actual pressure inside the carpal tunnel shows clear patterns. Keeping your wrist neutral (straight, with no bend) produces the lowest pressure. As the wrist extends backward, pressure climbs steadily. At 15 degrees of extension, typing pressure averages about 2.3 kPa. At 45 degrees of extension, it jumps to 4.0 kPa.
Side-to-side wrist angle matters too. Tilting the wrist toward the thumb side (radial deviation) generates higher pressure than a neutral or slightly pinky-side tilt. This is relevant for anyone who uses a mouse, holds tools at an angle, or plays certain musical instruments. Keeping your wrists as close to neutral as possible during sustained activities is one of the simplest ways to reduce cumulative stress on the median nerve.
Who Gets It Most Often
Carpal tunnel syndrome affects roughly 1% to 5% of the general population. Women develop it more frequently than men, partly because their carpal tunnels tend to be smaller and partly because of hormonal influences on fluid retention. The condition peaks between ages 40 and 60, though pregnancy-related cases obviously skew younger. People with multiple risk factors (for example, someone with a high BMI who also has diabetes and works a repetitive manual job) face compounding pressure on the nerve from several directions at once.