Carpal tunnel syndrome happens when the median nerve gets squeezed as it passes through a narrow passageway in your wrist called the carpal tunnel. About 5% of people worldwide develop it. The tunnel is formed by wrist bones on three sides and a tough band of tissue (the transverse carpal ligament) across the top, and anything that shrinks this space or swells its contents can compress the nerve and trigger symptoms.
How the Nerve Gets Compressed
The median nerve runs from your forearm through the carpal tunnel and into your hand, where it provides sensation to your thumb, index finger, middle finger, and part of your ring finger. Nine tendons travel through the same tight space. When pressure inside the tunnel rises, it restricts blood flow to the nerve, causing what’s essentially a slow-motion oxygen shortage. This ischemic compression is the core mechanism behind the numbness, tingling, and weakness that define the condition.
There are actually two specific pinch points inside the tunnel. One sits at the tunnel’s entrance near the wrist crease, where the tissue transitions from soft forearm fascia to the rigid ligament. The other is at the narrowest section of the tunnel, near the hook-shaped bone on the pinky side of your palm. Bending your wrist forward or backward increases pressure at both points, which is why symptoms often flare at night when people sleep with curled wrists.
Repetitive Motion and Workplace Exposure
Jobs that involve repeated wrist flexion, forceful gripping, or vibrating tools are well-established risk factors. A large Swedish registry study found that workers exposed to hand-arm vibration had a 61% higher risk of developing carpal tunnel syndrome compared to unexposed workers. At higher vibration levels, the risk climbed further, nearly doubling for men. On average, workers in the study had been exposed for about nine years before receiving a diagnosis.
The dose matters. Men working with the most intense vibrating tools (think jackhammers, grinders, chainsaws) had roughly 2.3 times the risk. Highly repetitive wrist movements, especially combined with a strong grip, are independently risky even without vibration. Assembly line work, meatpacking, and construction consistently show up in occupational studies.
What About Computer Work?
Despite its reputation, the evidence linking keyboard and mouse use to carpal tunnel syndrome is surprisingly weak. A systematic review of eight epidemiological studies found insufficient evidence to conclude that computer work causes the condition. Several studies actually found no increased risk, and one large population-based study showed that carpal tunnel prevalence went down as daily keyboard hours went up. A few studies did find a link with heavy mouse use (more than 20 hours per week), but methodological problems in those studies made the findings unreliable. The bottom line: computer work may contribute to wrist discomfort, but it hasn’t been established as a cause of true carpal tunnel syndrome.
Health Conditions That Raise Your Risk
Several systemic conditions make carpal tunnel syndrome more likely by either swelling the tunnel’s contents or narrowing the tunnel itself.
Rheumatoid arthritis is one of the clearest examples. The chronic inflammation it causes leads to swelling of the tendon linings inside the carpal tunnel, directly eating into the space available for the nerve. Over time, rheumatoid arthritis can also erode the wrist bones and loosen the transverse carpal ligament, collapsing the tunnel’s height and shrinking its volume even further. Unlike the slow, structural compression seen in most cases, rheumatoid-related carpal tunnel can develop quickly during an inflammatory flare.
Diabetes is another major risk factor. It makes nerves more vulnerable to compression, likely because elevated blood sugar damages the tiny blood vessels that supply the nerve itself. A nerve already running on reduced blood flow doesn’t tolerate even mild pressure well.
Hypothyroidism (an underactive thyroid) can cause fluid retention and tissue swelling throughout the body, including inside the carpal tunnel. Obesity plays a similar role: excess tissue increases pressure within the tunnel.
Pregnancy and Hormonal Changes
Carpal tunnel symptoms are remarkably common during pregnancy. Between 31% and 62% of pregnant women report symptoms like hand numbness and tingling, and electrical nerve testing shows median nerve changes in 7% to 43% of pregnancies. The culprit is fluid retention, which swells the soft tissues inside the tunnel and presses on the nerve.
The good news is that pregnancy-related carpal tunnel typically improves within a few weeks after delivery, closely tracking the loss of pregnancy weight and fluid. The less encouraging reality: symptoms linger longer than many women expect. The repetitive hand movements of nursing and newborn care, combined with leftover fluid retention and hormonal shifts, can delay full relief. Research shows that over 50% of women still report some symptoms a year after delivery, and about 30% still have them at the three-year mark.
Wrist Fractures and Acute Injuries
A broken wrist, particularly a fracture of the distal radius (the larger forearm bone near the wrist), can trigger carpal tunnel syndrome by displacing bone fragments into the tunnel or causing swelling that compresses the nerve. A study of nearly 40,000 patients with distal radius fractures found that 5.3% developed carpal tunnel syndrome within one year. The rate was higher among patients whose fractures required surgery (12%) compared to those treated with a cast alone (3%), likely because surgical cases involved more severe or displaced fractures that disrupted the tunnel’s geometry.
Other injuries that can narrow the tunnel include wrist dislocations, bone spurs from arthritis, and cysts or growths inside the tunnel itself.
Why Women Are More Affected
Women develop carpal tunnel syndrome at significantly higher rates than men. The leading explanation is anatomical: women tend to have relatively narrower carpal tunnels, which leaves less room to absorb any swelling or pressure changes before the nerve gets compressed. Hormonal factors compound this. Fluid shifts during pregnancy, menopause, and menstrual cycles all add temporary volume inside an already tighter space. The combination of a smaller tunnel and hormonal susceptibility helps explain why carpal tunnel syndrome peaks in women during their 40s and 50s.
Genetic Factors
Carpal tunnel syndrome isn’t inherited in a straightforward way, but genetics play a background role. The width of the carpal tunnel varies from person to person, and people born with narrower passages face higher baseline risk. Researchers have identified several genes involved in connective tissue structure, nerve function, and metabolism that appear to influence susceptibility. Having a close relative with the condition does increase your own risk, though the exact genetic contribution remains poorly understood. Think of it less as inheriting the condition and more as inheriting a wrist shape that leaves you with less margin for error.
How the Cause Is Identified
When you see a doctor about hand numbness or tingling, they’ll typically start with two physical tests. The Phalen test involves holding your wrists in a fully bent position for about a minute to see if symptoms appear. The Tinel test involves tapping over the nerve at the wrist to see if it triggers tingling in your fingers. Neither test is definitive on its own. The Phalen test correctly identifies about 57% of true cases and rules out about 67% of non-cases. The Tinel sign catches fewer cases (about 45%) but is better at ruling out false positives (78% specificity).
Because these physical tests have significant limitations, nerve conduction studies are often used to confirm the diagnosis. These electrical tests measure how quickly signals travel through the median nerve, and a slowdown at the wrist pinpoints the compression. Ultrasound imaging can also reveal nerve swelling or identify a specific cause like inflamed tendons or a cyst narrowing the tunnel.