Autism is caused by the way that the brain develops. In people with autism, the brain does not develop the same way it does in most people. The exact cause of ASD, however, is unknown. But there is evidence to suggest that both genetic and environmental factors contribute to the development of ASD.
If someone in your family has autism, it is more likely that other people in the family will also have autism. Research is also looking at the role of the environment in triggering autism, such as viral infections, complications during pregnancy and air pollutants. There is no evidence that autism can be caused by vaccinations, food, or other lifestyle factors.
