That's the million dollar question, isn't it? I've had it since birth. Some people develop it later in life.

The thing is, IBS is a term that represents many different gastrointestinal disorders that doctors don't know how to identify or treat (let alone cure!). My personal opinion is that most of it is caused by things like chemicals, preservatives, hormones, etc. in our food, water, and air, as well as the many prescription drugs we all end up taking for various ailments, especially antibiotics. Genetics play a role, as some people are obviously more prone to IBS than others.