With the rise of autism and autism awareness, the question of autism's origins often come up, and it is frustrating that there is not a definite answer. The short answer is that there is not one cause of autism, although it is primarily thought to be an abnormality in the physical brain or the brains ability to function. Scans of the brains of people with autism shows a marked difference in comparison to neurotypal brains. Some of their brains are even larger than neurotypal brains, and there is evidence that their brains process information in different ways when studying the path of neural processes. There is some evidence that autism can be genetic and runs in families. For instance, the progeny of someone with autism is more likely to show signs of autism. But in other cases it can be a congenital disorder, although a genetic basis is not confirmed through research yet, nor is it definite that a genetic basis is the only way that autism is caused.

There has been some correlation between autism and individuals with other disorders or diseases, such as tubercular sclerosis, phenylketonuria, Fragile X syndrome, and congenital rubella syndrome. It is also believed that some things ingested by the mother during pregnancy could contribute to causing autism, although again, there is no absolute confirmation within research. Other possibilities are environmental, such as the preponderance of toxins in our environment that were not as prevalent in the past. Many people with autism show sensitivity to these toxins and can suffer because of it. Most doctors suggest that the causes of autism are a combination of genetic/congenital and environmental influences, like many other disorders.

A few myths are prevalent about what causes autism. There was a claim in the past that mothers who did not give their children enough attention or affection caused the disconnected-like symptoms in autistic individuals. That claim has since been thoroughly debunked. Another is that the vaccine for measles, mumps, and rubella or the mercury that preserve vaccines have contributed to autism. Whether or not the mercury in vaccines causes autism is still a matter up for debate, but fortunately, thimerosal (the mercury-based preservative in vaccines) has been removed from most vaccinations. And the Center for Disease Control has engaged in its own studies regarding the MMR vaccine in doing so, they discovered that they might be a connection between gastronomical sensitivity to environmental toxins and autism, which supported the combination of genetic and environmental factors. But their findings concluded that the MMR vaccine did not cause autism. Some parents and small studies disagree, but it is worth noting that autism is not fatal, while measles, mumps, and rubella have the potential of being fatal in an already sensitive system.

The possibilities that vaccines caused autism did help researchers discover the possible link between immune sensitivity or deficiency and autism as well as gastro- and intestinal-sensivity and autism, so the controversy did some good for research on the causes of autism. At the present time, all that autism experts can offer is that the causes are mostly unknown, but likely environmental and genetic.