Note, I am not a doctor, and anyone reading this should consult a qualified physician if they are experiencing symptoms. Medscape.com describes the most common causes of this health issue, but for guitarists, pianists, office workers, etc., the likely culprit among them is calcium deposits, which can lead to Idiopathic Tumoral Calcinosis, the leading cause of Carpal Tunnel Syndrome. One way you can prevent or at least reduce the likelihood of getting Carpal Tunnel Syndrome if you are in one of those higher risk professions is to balance out your bone loss.
As you fret, or type, you are primarily using the muscles on the underside of your forearms, and as the muscles and tendons rub against the bone, it causes damage to the underside of the wrist. This is normal wear-and-tear for the body, and nothing to be concerned about with moderate activity. But for the professionals, the ones who spend hours per day, several days per week at their craft, the wear on the bones can be more dramatic.
As you wear down the bones in your wrist, your body has a natural repair system where it sends calcium to the affected area to rebuild the bone. Over time with repeated damage to just one side, the calcium will build up in deposits, which can put pressure on the median nerve (the actual source of pain associated with the syndrome). To help counteract this, there's a useful preventative step you can try involving a simple little exercise.
Just like a Gripmaster helps strengthen the muscles on the underside of the forearm, it is a good idea to also strengthen the muscles on the upper side of the forearm. This will help balance out any lop-sided damage to the wrist, and prevent calcium from collecting too much on just one side. There are many ways you can do this exercise, which is basically the opposite of a Gripmaster: instead of pushing your fingers down to compress a set of springs, you pull away to expand springs that are already compressed.
You can use springs from old exercise equipment, hanging scales, or anything else you can find of that nature; however, you can also simply use rubber bands (which may be safer to use and are much easier to find). Either use a single rubber band between the thumb and index finger, pull the fingers apart, then move to another finger; or, get a group of rubber bands all looped around your thumb, and loop one around each finger, and pull apart (working all the fingers at the same time). You'll have to play around with the tension, I believe it would be best to have a tension level equal to the tension you have to push down on your Gripmaster with.
You may be more comfortable with just one thick rubber band, or several smaller ones tied together... just add or remove bands until you get the tension to your liking. You obviously don't won't rubber bands that pull tight when your fingers are touching your thumb, but you will want them as short as possible, short enough that they are pulled tight without stretching while your fingers and thumb are essentially in the position they would be if you were resting them on a guitar neck. That position, with the thumb about 2-2.5" from each fingertip, should be the resting position.
Hopefully this can help someone who has not yet started showing signs of Carpal Tunnel Syndrome, who's profession (or hardcore hobby) is high-risk for the condition, to reduce or eliminate their likelihood of getting it. And again, as I stated above, this is not qualified medical advice, just a good idea based on documented evidence. Always consult your doctor before starting any new exercise regimen.
And to give credit where it's due, this idea did not come from me originally. This came from a discussion I had with a friend who has spent nearly 20 years studying anatomy to assist him as a licensed personal trainer (and is also a classically trained guitarist). I did a basic survey of several medical sites and papers to verify some of his claims regarding calcium deposits and bone loss, in addition to research I had done years before when I was incorrectly diagnosed with Carpal Tunnel Syndrome (research that helped me avoid a painful and unnecessary surgery for what turned out to be early onset arthritis). For me, playing guitar is not only mental and emotional therapy, it is also physical therapy to minimize joint pain. How great is it to have a doctor actually prescribe guitar playing?!?
*edit: For some reason the smiley isn't working, so I removed the PHP code.