- There's no single cause. Autism comes mainly from genes and how the brain develops before birth.
- Parenting doesn't cause autism. Nothing you did or didn't do made your child autistic.
- Large studies have found no link between vaccines and autism.
- The best next step isn't finding a cause. It's finding support that fits your child.
Is autism genetic?
Mostly, yes. Researchers agree that genes are one of the main causes of autism.1 A study of more than 2 million people in Sweden estimated that about 80% of the likelihood of autism comes from genetic factors.2
That doesn't mean there's one "autism gene." Hundreds of genes are involved, each adding a little. Many are common in the general population. Some children have a rare genetic change that neither parent has.
This is why autism often runs in families. After a child's diagnosis, many parents recognize some traits in themselves or relatives.
What else raises the likelihood of autism?
Researchers have found some factors that make autism more likely, though most children with them are not autistic:3
- Having a brother or sister who is autistic
- Having older parents
- Certain genetic conditions, such as fragile X syndrome or Down syndrome
- Being born with a very low birth weight
Some researchers are also studying how genes and conditions during pregnancy may interact, such as infections or certain medications.1
Do vaccines cause autism?
No link has been found. A Danish study followed more than 650,000 children and found no increase in autism after the MMR vaccine, including in children with autistic siblings.4 Dozens of other studies, covering millions of children, show the same result.
In 2025, some federal health messaging in the U.S. changed to question this. Major medical organizations, including the American Academy of Pediatrics, disagreed and continue to recommend routine vaccines. If you have questions, your pediatrician is the right person to ask.
Does Tylenol in pregnancy cause autism?
In 2025, U.S. federal officials announced plans to add a possible link to the acetaminophen (Tylenol) label. The evidence is mixed, and the best-designed studies don't show that acetaminophen causes autism.
A 2024 study of about 2.5 million children in Sweden compared brothers and sisters. When siblings were compared, there was no link between acetaminophen use in pregnancy and autism.5 The American College of Obstetricians and Gynecologists says acetaminophen remains an appropriate choice for pain and fever in pregnancy, used as needed.6
What doesn't cause autism?
- Parenting style, discipline or attachment
- Too much or too little attention as a baby
- Screens. Research hasn't shown that screen time causes autism (more in Can screen time cause autism?)
- Food or diet after birth
Does knowing the cause change what helps?
Usually not. For most children, testing won't find a single cause. What helps is the same either way: understanding your child's strengths and needs, and supports like speech therapy, visual routines and help at school.
Some doctors recommend genetic testing after a diagnosis, because it can find related conditions and help with family planning. Ask your pediatrician whether it makes sense for your child.
What can I do next?
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