There is little doubt that heredity is a major factor in developing carpal tunnel syndrome. Your genetics determine 3 important biological results:

1. The size and shape of your carpal tunnel space. 
2. How susceptible your median nerve is to damage. 
3. How resilient your tendons are to stress. 

Tendons require top level performance to maintain their lubrication and strength. At the biochemical level, this involve efficiently replacing worn-out components, like surface proteins. Even the slightest defect in that maintenance process can trigger formation of adhesions. This can result in tendon irritation and swelling. Such swelling, of course, is one of the main underlying carpal tunnel syndrome causes. 

All anatomy and biochemical activity is passed down from generation to generation. Therefore, so are the consequences of biochemical and anatomical defects. So if you have a close family relative (parent or sibling) with carpal tunnel syndrome, your risk of also developing it increases several fold.

Carpal tunnel syndrome is far more common in women than men. In fact, it's so much more prevalent in women that some medical scientists argue it's a true female disorder. 

This association may be due to the anatomically smaller diameter of the carpal tunnel space in women compared to men. Also, there are generally greater hormonal fluctuations in women. 

This is highlighted by the fact that nearly half of pregnant women suffer with carpal tunnel symptoms, most likely due to fluid retention. (Pregnancy is discussed separately below.)

Pregnancy deserves its own section when it comes to carpal tunnel syndrome. Causes and consequences of hormonal imbalance and fluid retention are directly related to acquiring this disorder. 

About 50% of all pregnant women experience signs and symptoms of carpal tunnel syndrome. This is most pronounced in the third trimester. 

The reason for this association is direct. Pregnancy often induces abnormal fluid accumulation - most frequently in the ankles and wrists. So it's no wonder that fluid pressure can add to the compression of the median nerve inside the wrist joint.

In approximately 50% of pregnant women with carpal tunnel syndrome, symptoms will disappear within 3 months of childbirth. In another 25%, it can take up to a year for symptoms to disappear completely. The remaining 25% may see symptoms of carpal tunnel syndrome last three or more years after childbirth.

The fundamental problem in carpal tunnel syndrome is that the median nerve is crushed inside the narrow space deep inside the wrist joint. So it stands to reason that the smaller or more narrow the space, the greater the probability that the median nerve will become crushed. 

So it's no surprise that small-framed individuals are more prone to this disorder. In fact, just look at the higher probability of females who suffer from carpal tunnel syndrome. The relatively smaller female frame may be a key factor for the higher incidence of the disorder in women.

It's not uncommon for people with sudden mechanical trauma to their hand, wrist or forearm to experience carpal tunnel syndrome. Causes of trauma usually include motor vehicle accidents, falls, and osteoporosis-related injury.

There could be potentially many reasons why trauma can induce carpal tunnel syndrome. In most instances, the trauma likely rearranges an already tightly packed carpal tunnel space inside the wrist joint. So it's not inconceivable that even a minor alteration of that anatomy can have a huge effect on the total volume of the carpal tunnel space.

In addition, any trauma can potentially damage the median nerve, even in a seemingly minor way. Nerves are exquisitely sensitive to injury by mechanical pressure. So even a transient crushing or loss of blood supply can have huge consequences on the median nerve's health.

For decades, scientists and doctors have noticed a strong association between carpal tunnel syndrome and how a patient uses their hands. More often than not, one of the primary carpal tunnel syndrome causes points directly to repetitive hand and finger stress. 

Actually, many scientists classify carpal tunnel syndrome as a type of Repetitive Stress Injury (RSI).  This happens whenever you perform the same activity, over and over, with your hand and fingers. 

Certain occupations are well-known for being at high risk for developing carpal tunnel syndrome. That's because they require performing one of the following activities which are stressful to the hand or fingers:

1. Fast finger movements (typing, gaming, sewing)
2. Forceful grasping (using a hammer, shoveling, hairdressing)
3. Rapid grip-and-release activity (grocery stocking or cashiering, automotive, bricklaying)

Any one of the above activities can produce an RSI. The range and variety of occupational tasks between light and fast movement to slow and heavy activity is enormous. That's why carpal  tunnel syndrome affects practically every occupation.

Patients who have rheumatoid arthritis (RA) have a much higher probability of developing carpal tunnel syndrome. Causes and links in this relationship are not well understood. However, the inflammatory effect of RA may somehow transmit to the tendons inside the carpal tunnel space. 

The RA may add to already inflamed tendons. The addition of "extra" inflammation could be just enough for any swelling to fully crush the median nerve and produce symptoms.

Sometimes, it's difficult for doctors to initially determine if the pain, numbness or tingling is a result of arthritis or carpal tunnel syndrome. Causes and pathologies are very different, but symptoms can be almost identical.

People who use vibrating hand tools are at high risk for developing carpal tunnel syndrome. But there's an associated disorder that's even worse: vibration syndrome. This is also known as Hand Arm Vibration Syndrome (HAVS), vibration white finger, and Raynaud’s phenomenon (or disease). It comes about from chronic use of vibrating tools and equipment.

The reason vibration syndrome is worse than carpal tunnel syndrome is that it's not reversible. For reasons still not well understood, the vibration causes the peripheral nerves in the hand to degenerate and die. If the patient stops engaging in the use of the vibrating tool, the condition does not worsen. But it does not reverse, either. 

Vibration syndrome can happen after exposure to vibration in as short as one year. Occupations infamous for this condition are any which require vibrating hand tools and power tools. In particular, gas-powered chain saws, rock saws, and pneumatic hammers are particularly dangerous. The CDC warns of this problem. It recommends wearing protective equipment like thick gloves or else modify the equipment to minimize vibrations. 

Nerves can be damaged by various kinds of trauma (see above) and by certain chronic illnesses. In fact, diabetes is infamous for producing neuropathy or nerve damage. Diabetes (discussed under "Metabolic disturbances" below) commonly produces neuropathy in the lower limbs. But it's just as likely to cause neuropathy of the median nerve in the wrist. This can result in carpal tunnel syndrome. 

Diabetes is just one illness that can result in neuropathy. Certain autoimmune diseases can do the same. This is when the immune system attacks your body's own tissues. One of those tissues can be the median nerve, and the result is neuropathy. In particular, Sjogren's syndrome, lupus, and rheumatoid arthritis (discussed separately above) are known risk factors.

Finally, nerve damage can result from exposure to toxins. These include industrial chemicals in addition to heavy metals like mercury and lead.

Certain illnesses cause metabolic disturbances throughout the body. The most common (aside from pregnancy, discussed above) is diabetes. 

Most diabetic patients are prone to peripheral neuropathy. Commonly, diabetic neuropathy is most noticeable in the limbs. 

Diabetic patients develop carpal tunnel syndrome symptoms the same way they're caused by any other mechanism. That is, swollen tendons crush the median nerve. But in diabetes, the median nerve is far more sensitive to injury. Even the smallest amount of tendon swelling can result in median nerve damage.

What's interesting is that carpal tunnel syndrome can occur in patients long before diabetes is diagnosed. One study shows carpal tunnel syndrome preceding a diagnosis of diabetes by 10 years.

Also, metabolic syndrome is diagnosed in carpal tunnel syndrome patients more than the general population. This means that somehow, the mechanisms that produce metabolic syndrome impact the environment inside the carpal tunnel passageway.

Anyone can develop carpal tunnel syndrome at any age. However, pre-adolescent symptoms are rare. Population studies have shown that the age distribution of carpal tunnel syndrome has 2 peaks.

Individuals are more likely to develop carpal tunnel syndrome either between ages 50–54 years old or between ages 75–84 years old. The reason for this "bimodal age distribution" is not well understood. However, it may have its basis in comorbidities. That's when there's one or more additional disorders occurring with a primary illnesses (like carpal tunnel syndrome).

It's unknown to what extent age-related comorbidities can affect the median nerve to make it more susceptible to carpal tunnel syndrome.

Patients who have carpal tunnel syndrome have a 34% probability of being obese. But is obesity part of what causes carpal tunnel, or does carpal tunnel and chronic pain contribute to overeating and subsequent obesity? No one knows for sure. 

There is one thing for certain. People with a BMI greater than 30 are 2.5 times more likely to acquire carpal tunnel syndrome than normal weight people. 

People who consume too much alcohol have a higher chance of getting carpal tunnel syndrome. The reason is due to simple nerve toxicity.

All alcoholic products are toxic to nerves. That means that high volumes of alcohol can cause neuropathy or damage to the median nerve. 

Even though alcohol may be what causes carpal tunnel in heavy drinkers, the interesting fact is that it’s reversible. When patients stop drinking, the neuropathy disappears. And so do carpal tunnel symptoms.

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There is a complex yet definite relationship between stress, anxiety & carpal tunnel syndrome. Scientists are still trying to work out the details, but it's clear that people with emotional stress are more prone to developing carpal tunnel syndrome.

The relationship is likely due to muscle strain. Emotionally stressed individuals often feel their muscles are tense. The tense muscles can alter how they use their hands. 

For instance, emotional anxiety can cause muscle tension in the shoulders. This causes the person to adjust their sitting posture to relieve the tension. 

Often, such postural changes put enormous biomechanical strain on the upper body. Slouching is a perfect example. The slouchng posture transmits abnormal mechanical forces to the arm and wrist. As we already know, even the slightest deviation for the normal state can cause trauma to the median nerve. As a result, it becomes susceptible to crushing and, consequently, carpal tunnel syndrome.

Studies have shown that chronic liver disease such as hepatitis or cirrhosis can result in damage to peripheral nerves, like the median nerve. In fact, one study found the prevalence of carpal tunnel syndrome in liver disease patients can be as high as 33%.

The same study also found significant correlation between the severity of carpal tunnel syndrome and the severity of the liver disease. However, like many possible carpal tunnel syndrome "causes" this relationship should not be construed as a direct cause-and-effect phenomenon. Too little is known about this relationship other than the correlation between carpal tunnel syndrome and liver disease.

The National Institute of Neurological Disorders and Stroke has established a link between hypothyroidism (underactive thyroid) and carpal tunnel syndrome. Patients with hypothyroidism are 2-5 times more likely to develop carpal tunnel syndrome compared to the normal population. 

The link between these two conditions is relatively easy to understand. Hypothyroidism is a hormonal disease that has many biochemical consequences. Most notably, it can cause fluid retention. It also affects the chemistry of all peripheral nerves, including the median nerve. 

Therefore, fluid pressure is more likely to build up inside the carpal tunnel space and cause compression of the median nerve. In addition, the median nerve can be made more sensitive to compression damage. Even a slight increase in pressure can therefore result in severe crushing injury to the median nerve.

There are some medical conditions definitely associated with carpal tunnel syndrome. But like so many carpal tunnel syndrome causes, exactly why they produce symptoms is unknown.

The most common medical conditions (not described elsewhere in this review) are kidney failure, menopause, gout and lymphedema.

Kidney failure causes a myriad of fluid balance disturbances. Fluid retention is almost always a consequence. So it's not difficult to see how kidney-induced fluid pressure accumulation in the carpal tunnel space can produce symptoms of carpal tunnel syndrome.  

Likewise, menopause is known to disturb the body's fluid balance. Abnormal distribution of fluid to the carpal tunnel space can easily cause fluid pressure build-up. This in turn, crushes the median nerve and produces the symptoms of carpal tunnel syndrome. However, recent studies have challenged the role of menopause in causing carpal tunnel syndrome. 

Gout is also associated with carpal tunnel syndrome. One study even suggests that symptoms of carpal tunnel syndrome can be the first signs of gout.

Lymphedema refers to swelling that generally occurs in one of your arms or legs. Sometimes both arms or both legs swell. Lymphedema most commonly happens when lymph nodes are either damage or removed as part of treatment for cancer. 

In such circumstances, the lymphatic system can become locked, preventing lymph fluid from draining out of tissues. The result is fluid accumulation and swelling. If this occurs in the wrist, the result can be carpal tunnel syndrome.

One study showed that lymphedema patients were 2 times as likely to develop carpal tunnel syndrome. However, newer research is challenging the direct relationship between lymphedema and carpal tunnel syndrome.

Sometimes one of the key causes of carpal tunnel syndrome is related to medications the patient is taking. The primary drugs most commonly linked to developing carpal tunnel syndrome are aromatase inhibiting antiestrogens such as anastrozole (Arimidex), exemestane, and letrozole. These drugs are used to treat some breast cancers.

In addition, disphosphonates (used in osteoporosis), some oral anticoagulants, and some antiretrovirals also are linked to developing carpal tunnel syndrome. 

Research has now established why these compounds increase the probability of acquiring symptoms of carpal tunnel syndrome. It's likely they are toxic (to some degree) to peripheral nerve tissues. Therefore, the median nerve can be made ultrasensitive to trauma, as might occur with repetitive stress.

Chronic fatigue syndrome (CFS)  is also called myalgic encephalomyelitis (ME) or ME/CFS. It's actually a cluster of complicated chronic illness afflicting over 1 million Americans. Females are 2-4 times more likely  to be diagnosed with it. 

The wide range of ME/CFS symptoms can include arm and hand pain. There has not been a research study performed to date to point to ME/CFS as one of the carpal tunnel syndrome causes. 

However, a recent study has shown that symptoms of carpal tunnel syndrome are more than twice as likely to occur in patients who have symptoms of chronic fatigue syndrome.

Anyone diagnosed with fibromyalgia knows the symptoms: widespread pain, headaches, fatigue, and a host of other crippling symptoms. Each one can make life miserable. But another association with fibromyalgia is carpal tunnel syndrome. 

Fibromyalgia and carpal tunnel syndrome share similar symptoms. Also, numerous surveys and research studies have shown a definite pattern. 

At least a quarter of patients with carpal tunnel syndrome also have fibromyalgia. Some estimates are up to a third. What's most fascinating is when only women patients who have carpal tunnel syndrome are calculated, over 50% of them also have fibromyalgia.

The relationship between the two disorders is not well understood by doctors. The lack of knowledge is mostly due to fibromyalgia's causes being almost completely shrouded in mystery.

For nearly 3 decades, scientists have shown a parallel between having Lyme disease (Lyme borreliosis) and carpal tunnel syndrome. In fact, the association is extremely high.

Carpal tunnel syndrome is present in about 25% of patients with late Lyme disease. Exactly why a huge proportion of patients who have late Lyme disease also develop carpal tunnel syndrome is unknown.

Patients undergoing chronic dialysis are more prone to compression of the median nerve. The reason is not clear, but may be related to a dialysis shunt or fistula causing edema or vascular insufficiency.

Also, patients who have renal (kidney) failure can develop amyloid disease. Amyloid is an abnormal protein. It can be deposited in any tissue, like tendons and nerves. Patients with renal failure can have amyloid infiltrate their flexor tendon sheaths. The amyloid causes irritation, swelling, and ultimately compression on the median nerve. Carpal tunnel symptoms can result.

Since carpal tunnel syndrome is a compression neuropathy, it should come as no surprise that a tumor in the wrist can also compress the median nerve. Note that a tumor can only mimic carpal tunnel symptoms. The actual carpal tunnel syndrome cause is not due to median nerve compression by tendons, but by a tumor.

The NIH advises that doctors must consider the possibility of a tumor during examination of the wrist. An initial diagnosis starting with feeling for a mass in the wrist is advised.