The exact cause of autism is currently unknown.

The exact cause of autism is currently unknown.

Autism is a complex neurodevelopmental condition. The causes are still being investigated.

Current evidence suggests that autism may be caused by many factors that affect the way the brain develops.

These include:


Most researchers believe that certain genes a child inherits from their parents could make them more likely to have autism. This is called a genetic predisposition.

Autism is known to run in families. For example, younger siblings of autistic children can also be autistic. It's also common for identical twins to both be autistic.

Although scientists are still trying to identify the genes involved, signs of autism may be a feature of some rare genetic syndromes.

These include:

Environmental triggers

Very few conditions are caused only by genes. Most are caused by a combination of genes and environmental factors or triggers.

Environmental triggers include lifestyle factors, such as diet and exercise.

Researchers believe that there are some possible triggers that may increase the likelihood of being autistic.

These include:

  • being born prematurely (before 35 weeks of pregnancy)
  • being exposed to alcohol in the womb
  • being exposed to certain medicines, such as sodium valproate (sometimes used to treat epilepsy), in the womb

What does not cause autism

In the past, a number of things were linked to autism, but extensive research has found no evidence to suggest that any of these contribute to the condition.

These things include:

  • the MMR vaccine
  • thiomersal – a mercury compound used as a preservative in some vaccines
  • the way a person has been brought up
  • diet, such as eating gluten or dairy products
  • pollution
  • maternal infections in pregnancy

Page last reviewed: 03/02/2019
Next review due: 03/02/2022