What causes CTS and who is more likely to develop it?

Genetic predisposition. The carpal tunnel is smaller in some people than others.
Repetitive Movements. People who do the same movements with their wrists and hands over and over may be more likely to develop CTS.

People with certain types of jobs are more likely to have CTS, including manufacturing and assembly line workers, grocery store checkers, violinists, and carpenters. Some hobbies and sports that use repetitive hand movements can also cause CTS, such as golfing, knitting, and gardening. Whether or not long-term typing or computer use causes CTS is still being debated. Limited research points to a weak link, but more research is needed.
Injury or Trauma.

A sprain or a fracture of the wrist can cause swelling and pressure on the nerve, increasing the risk of CTS. Forceful and stressful movements of the hand and wrist can also cause trauma, such as strong vibrations caused by heavy machinery or power tools.
Pregnancy.

Hormonal changes during pregnancy and build up of fluid can put pregnant women at greater risk of getting CTS, especially during the last few months. Most doctors treat CTS in pregnant women with wrist splits or rest, rather than surgery, as CTS almost always goes away following childbirth.
Menopause. Hormonal changes during menopause can put women at greater risk of getting CTS. Also, in some postmenopausal women, the wrist structures become enlarged and can press on the wrist nerve.

Breast Cancer. Some women who have a mastectomy get lymphedema, the build-up of fluids that go beyond the lymph system's ability to drain it. In mastectomy patients, this causes pain and swelling of the arm. Although rare, some of these women will get CTS due to pressure on the nerve from this swelling.

Medical Conditions. People who have diabetes, hypothyroidism, lupus, obesity, and rheumatoid arthritis are more likely to get CTS. In some of these patients, the normal structures in the wrist can become enlarged and lead to CTS.
Also, smokers with CTS usually have worse symptoms and recover more slowly than nonsmokers.