What is the cause of autism?

Cute thinking kid girl in glasses with empty bubble looking

What is the cause of autism?

The short answer is, autism is caused by a combination of factors.

We do know there is no single cause of autism. Our best research tells us that it’s a combination of both genetic and environmental factors. Let’s take a look at what we do know…

Genetic cause of autism

We know that autism runs in families. A study published by the American Medical Association looked at over 2 million individuals from 5 different countries and determined that autism is 80% due to genetic factors. This means that 80% of autism can generally be attributed to genetics, while only 20% can be attributed to environmental factors. We also know from twin studies that, if one twin has autism, the other twin’s likelihood of having autism is somewhere between 64% and 91%.

If a parent is a carrier of one of these autism genes, they may pass it along to their children, even if they do not have autism themselves. Furthermore, if both parents are a carrier, the combination of their genetics may give rise to autism in their child.

environmental cause of autism

Let’s be clear: when we say “environmental” we don’t mean global warming, pesticides, or fluoride in your toothpaste. In the scientific literature, “environmental” simply means “non-genetic.” For example, for autism, this could be preterm delivery, parental age, multiple pregnancies, etc. In fact, there is research supporting the following environmental risk factors:

What is not a cause of autism?

We know that vaccines do not cause autism. Full stop. Read about vaccines and autism at our other post here.

The American Academy of Pediatrics maintains a list of all of the research debunking the link between vaccines and autism. Quite simply, we know that vaccines do not cause autism. We suggest you speak to your pediatrician about vaccination and follow their advice.


Whatever the case, parents should know that there is a lot of reason to be hopeful for their children. People with autism often go on to live happy and healthy lives filled with all the things they enjoy. Furthermore, the neurodiversity movement is achieving more widespread acceptance of autism, which means your child is very likely to have a happy future!

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