Perhaps the greatest factor in causing carpal tunnel syndrome is genetics. If a close family member has or had carpal tunnel syndrome, chances are extremely high you will get it also. 

Genetics determines how sensitive your nerves are. Genetics also determine the strength of your tendons and the shape of your wrist joint. These factors all contribute to the probability of getting carpal tunnel syndrome.

All doctors know that women are much more prone to getting carpal tunnel syndrome than men. Some estimates make women over 20 times more susceptible.

So what female characteristics cause carpal tunnel? The answer is unknown. But scientists speculate the relationship is due to the smaller wrists in women. In addition, women experience greater hormonal fluctuations than men. This disturbs fluid balance which is an underlying contributor to carpal tunnel syndrome.

Ask any doctor, “What causes carpal tunnel in women?” and the answer will be pregnancy. Pregnancy is well-known to be one of the greatest contributors to carpal tunnel syndrome in women. The reason? 

Fluid retention is elevated, particularly in the joints like the ankles and wrist. The disturbance in fluid retention is due to hormonal fluctuations. 

Carpal tunnel syndrome is fundamentally due to pressure on the median nerve, deep inside the wrist joint. If fluid pressure accumulates in the wrist joint, it will exert pressure on the median nerve, ultimately crushing it. That’s when symptoms appear.

Half of all pregnant women will experience some signs of carpal tunnel syndrome. It’s most prevalent in their third trimester.

Half of those women will see their symptoms spontaneously disappear within a few months after delivery. The other half may see symptoms dissolve over 12 months. The unfortunate remaining 25% will not see symptoms disappear at all without treatment.

Studies have shown that people with small physical frames are more prone to getting carpal tunnel syndrome. The reason is likely due to the overcrowding inside the wrist joint to begin with. 

The overcrowding more easily exerts pressure on the median nerve. It stands to reason that a smaller diameter wrist joint merely adds to the overcrowding. Ultimately, the median nerve becomes crushed more easily.

This may also be the underlying mechanism for what causes carpal tunnel in women more frequently than men. Their generally smaller frames (and wrists) increase the probability that the median nerve can be crushed more easily.

Your chances of acquiring carpal tunnel syndrome after a hand or wrist injury increase dramatically. A fracture or sprain can bring it on any time from weeks to months after the trauma.

The reason injury has such a great impact on getting carpal tunnel syndrome is likely due to the anatomy of the carpal tunnel space. This is a delicate area with complex construction. And it’s tightly packed with tendons and the median nerve. 

A slight change in the anatomy, as with an injury, can alter that delicate anatomy. And since the median nerve is the most sensitive structure inside the wrist joint, it stands to reason it will be most affected by an injury.

It’s no secret that certain occupations produce a higher number of carpal tunnel syndrome cases. What those occupations usually have most in common is they require repetitive stress of the fingers and hand.

Repetitive strain injury (RSI) is often cited as one of the most important factors in acquiring carpal tunnel syndrome. And there’s no doubt that repetitive stress and strain can make tendons inflame and swell. As a result, the swollen tendons exert pressure on the median nerve, and carpal tunnel symptoms result.

You can repetitively stress your fingers and hands in three major ways: move fingers rapidly and repetitively, grasp tightly for long periods of time or grasp and release constantly. Either activity can cause tendon inflammation if it persists for longer than several minutes at a time.

If you have rheumatoid arthritis then your probability of acquiring carpal tunnel syndrome increases many fold. The reason for this is not understood.

But rheumatoid arthritis is an inflammatory disease. And carpal tunnel syndrome is – at its core - due to inflamed tendons. So the current thought is that the mechanism which causes rheumatoid arthritis is similar to that which causes carpal tunnel syndrome.

A main cause of carpal tunnel syndrome on the job is using vibrating hand tools. Jobs where use of electric saws, drills, and motors have an extraordinarily high incidence of this disorder. This is why it’s important to protect your hands in such occupations. Taking breaks, using gloves or using padded protective tools will help a great deal.

A similar condition to carpal tunnel syndrome is called Hand Arm Vibration Syndrome or HAVS. It also goes by the name of "White Finger” or Raynaud’s disease. Unlike carpal tunnel syndrome, HAVS is progressive and not reversible.

When tendons swell inside the carpal tunnel, they crush and damage the median nerve. But the median nerve can also be damaged in other ways. Chronic illnesses also cause damage to peripheral nerves (called neuropathy) including the median nerve.

Chief among the illnesses causing neuropathy is diabetes. In fact, it’s such a major factor in what causes carpal tunnel syndrome that it has a separate section below. Other chronic illnesses that can cause carpal tunnel syndrome include lupus, Sjogren’s syndrome, and rheumatoid arthritis (discussed above).

You can also acquire a neuropathy by poisoning from toxins. The most serious neurological consequences result from exposure to heavy metals such as lead, cadmium, and mercury.

Diabetes is the most prevalent metabolic disturbance on earth. One of the effects of diabetes is peripheral neuropathy or damage to nerves. Therefore, diabetic neuropathy of the median nerve can produce carpal tunnel syndrome.

Often, carpal tunnel syndrome symptoms appear even before the patient knows they have diabetes. In fact, the lag time between having carpal tunnel syndrome and getting a diabetes diagnosis can be as much as ten years.

Diabetes causes nerves to be more sensitive. This is why the median nerve, even when slightly irritated by swollen tendons, will react and produce symptoms. 

The other metabolic condition which is a major factor in what causes carpal tunnel is metabolic syndrome.  It’s actually a cluster of factors associated with cardiovascular disease. And it increases the likelihood of developing not only carpal tunnel, but also stroke, heart disease, diabetes – and possibly all of these disorders simultaneously.

If you’re older than 74, your chances of developing carpal tunnel syndrome nearly double when comared to younger people. With advancing age, the ability to heal diminishes. So if tendons are stressed and strained, they will take longer to heal. 

That means there is a higher likelihood that tendons will remain inflamed and swollen longer. This then results in pressure on the median nerve and the resulting symptoms of carpal tunnel syndrome. 

But some doctors believe the association between age and carpal tunnel is more related to having other disorders that statistically come with age. For instance, rheumatoid arthritis and diabetes (or both) may contribute to getting carpal tunnel syndrome then merely old age. Obviously, more research is needed in this field.

The prevalence of obesity in carpal tunnel syndrome patients is about 34%. But is obesity one of the many possible carpal tunnel syndrome causes or does chronic carpal tunnel pain merely contribute to overeating? Scientists don't presently know.

This relationship is important for doctors to understand during their initial diagnosis of carpal tunnel syndrome. The only fact we can state for certain is obese individuals (with a BMI grater than 30) are 2.5 times more likely to be diagnosed with carpal tunnel syndrome than slender or normal weight individuals. 

Patients who drink excessive amounts of alcohol increase their risk of developing carpal tunnel syndrome. The direct reason for this is because drinking alcohol over a long period of time can result in neuropathy (nerve damage).

Alcohol is toxic to nerve tissues. And it's alcohol's toxic effect on nerves that makes them more sensitive to trauma. So if the patient drinks chronically and also engages in other high risk activities (like repetitively stressing their hand) then carpal tunnel syndrome has a higher probability of occurring.

But alcohol toxicity is reversible. Those who quit drinking are able to halt any further nerve damage. Most fascinating of all, patients who quit drinking are also able to eliminate their carpal tunnel symptoms.

Doctors have long known that there’s a link between emotional stress and carpal tunnel syndrome. That means people with anxiety and stress are more likely to develop carpal tunnel syndrome. But just like with alcohol consumption, is the emotional stress what causes carpal tunnel, or does the pain of carpal tunnel add to (and escalate) already existing stress and anxiety? Nobody knows for sure.

Another related factor is that emotionally stressed people tense their muscles. Muscle tension in the neck, shoulders, and back transmit to the hands. This then alters the normal anatomy of the wrist joint. And being a complex anatomical area, just a small displacement of structures in the wrist joint can cause pressure on the median nerve.

The best example of this is when a person displays poor sitting posture. Because of their stress (from work, home, etc.) they concentrate less on posture and more on getting the job done. Consequently, they hunch or slouch. Both of these poor postures transmit forces to the hand. As a result, the median nerve can become crushed. Then carpal tunnel symptoms follow.

The more common diseases of the liver are cirrhosis and hepatitis. Research has shown that either one of these conditions can cause neuropathy. In fact, doctors have evidence to show that in people with liver disease, there is a 33% incidence of carpal tunnel syndrome.

What’s more interesting is that there’s a direct relationship between how advanced the liver disease is and how severe the patient’s carpal tunnel syndrome. But is liver disease a direct factor in what causes carpal tunnel or is the liver disease somehow a byproduct of the neuropathy? This is unknown.

There is a definite association between hypothyroidism and carpal tunnel syndrome. If you have hypothyroidism then the probability is up to 5 times higher that you’ll also develop carpal tunnel. 

This association is clearer than most other risk factors. The thyroid controls fluid accumulation in the body. An underactive thyroid can throw that fluid balance off considerably. This then has consequences on all of the body’s tissues, especially nerves like the median nerve.

Unchecked fluid balance can easily cause nerves to be more sensitive. That means any excessive compression or stress on the nerve (from tendons) can result in neuropathy. This will produce all of the symptoms of carpal tunnel syndrome.

There are more conditions that can directly or indirectly cause carpal tunnel syndrome. These are less common than those discussed above. They include:

• Gout
• Kidney failure
• Lymphedema
• Menopause

In discussing what causes carpal tunnel, we must include certain prescription drugs. These drugs can elevate your chances of getting carpal tunnel syndrome several fold.

Chief among them are aromatase inhibiting antiestrogens used to treat breast cancer. They are anastrozole (Arimidex), letrozone, and exemestane. There also are reports of carpal tunnel syndrome occurring in patients taking disphosphonates for osteoporosis.

Chronic fatigue syndrome (CFS - also called myalgic encephalomyelitis) affects over a million people in the USA. Women are far more likely to have CFS.

The association between carpal tunnel and CFS is not clear. But research shows that carpal tunnel syndrome is over two times more likely to occur in people with CFS.

Carpal tunnel syndrome and fibromyalgia have similar symptoms. In fact, sometimes one disorder is misdiagnosed for the other. 

But the statistics are amazing. About 25% of people with carpal tunnel also suffer from fibromyalgia. The greatest proportion of people who have both conditions are women. Just how these two conditions are related is a mystery.

There is a strong relationship between having carpal tunnel syndrome and Lyme disease. However, the reason for the association is not clear.

Lyme disease can result in many types of secondary illnesses. In particular, if you have Lyme disease, then your chances of developing carpal tunnel syndrome skyrocket. Statistically, a quarter of people with Lyme disease also have carpal tunnel syndrome.

People who receive dialysis on a chronic basis are more susceptible to getting carpal tunnel syndrome. There are two major theories about why this is so.

A dialysis shunt can cause edema. This edema (swelling) can then transmit to the wrist joint and compress the median nerve.

On the other hand, kidney disease can produce amyloid disease. This results in abnormal protein being deposited in tissues like tendons. The protein causes irritation on tendons. As a result, the tendons ultimately inflame and swell. If this happens in the wrist joint, the median nerve will become crushed by the tendons, thereby resulting in carpal tunnel syndrome.

Any time a tumor grows in the body, it pushes aside normal, healthy tissue. So if a tumor grows in the wrist area, it will also push aside tendons and the median nerve.  The result is a compression neuropathy.

Since the median nerve is sensitive to pushing and crushing, any nearby tumor can also cause compression trauma to the nerve. The result is symptoms of carpal tunnel syndrome. And the symptoms will be identical to carpal tunnel acquired from, say, repetitive stress.

This is why a careful examination of the wrist is needed when symptoms arise. A tumor must be ruled out before the doctor makes a diagnosis of carpal tunnel syndrome.