It is known that there is a mix of genetic and environmental factors that cause Autism. There are many studies on specific environmental factors that have been found to increase the probability, but it isn't simple at all because the overwhelming majority of kids exposed to those factors won't end up with Autism.

I definitely believe that the increasing numbers on Autism are just because we are getting much better with diagnosis. The spectrum is HUGE - kids aren't going to have the same traits or the same issues or strengths when they are on the spectrum. But our education system has gotten much better with identifying several "red flags", and the early intervention programs are much better than they used to be.