Causes of Autism Spectrum Disorders

Causes of Autism

Many parents wonder whether something they did—or didn't do—might have caused their child's autism. While it is possible to nail down the cause of autism in some children, most parents will never find a definitive answer to their question.

Though quite a few rare genetic disorders and toxic exposures are known to cause autism (or "autism-like symptoms" that may be misdiagnosed as autism), most cases are considered "idiopathic," meaning "without known cause." 

A Controversial Topic

As you explore the question of "what causes autism," you are likely to come across many individuals who are absolutely certain they know the answer. It's important to know, though, that the subject is highly controversial and one parent's (or researcher's) passionate statements doesn't take the place of solid research.

Known Causes

There are a few relatively rare known causes of autism, including:

In addition to these rare, documented causes, some studies point to a higher risk of autism being associated with older parenthood, certain types of pollution, and a variety of other issues.

Association, however, is not the same thing as causation. And it seems likely, for example, that older parents are associated with autism because they are more likely to be autistic themselves and thus have a harder time finding a mate.


Researchers are certain that some cases of autism have a genetic basis. So, it is quite possible that genetics are involved with all cases of autism.

Many studies have shown that parents from families with autistic members are more likely to have autistic children. In addition, families with one autistic child are at increased risk of having more than one autistic child.

Interestingly, however, "genetic" and "hereditary" are not the same thing. Studies have shown many cases of "spontaneous" genetic mutation associated with autism. Spontaneous genetic mutation, as the name implies, just happens—usually for unknown reasons. In other words, a child can be born with genetic differences which are not inherited, but which may be associated with autism.

Brain Structure

Some researchers have found differences between the autistic brain and the typical brain. Autistic individuals seem to have larger brains. They also seem to process information differently. In other words, their brains are "wired" differently.

 Research on this issue is ongoing, with intriguing findings coming out of top institutions.

In recent years, researchers have experimented with a treatment called transcranial magnetic stimulation (TMS), which stimulates nerve cells in the brain. TMS has been successful in treating depression and shows promise as a tool for treating some symptoms of autism.

Factors That Do Not Cause Autism

While we don't always know what causes autism, researchers have done a great deal of work to determine that certain things do NOT cause autism.

Why work so hard to disprove theories? Because several theories related to autism have led to untold emotional pain, risky behavior, and even some deaths.


For a period of time during the 1990 's and early 2000's , two theories appeared to link autism and vaccines.

  1. The first theory suggested that the MMR (Mumps-Measles-Rubella) vaccine may cause intestinal problems leading to the development of autism.
  2. The second theory suggested that a mercury-based preservative called thimerosal, used in some vaccines, could be connected to autism.

    The medical community has soundly refuted these theories, but a very passionate group of parents and researchers continue to disagree based on anecdotal evidence.

    In short, NO—vaccines do not cause autism. If you had your child vaccinated, you did not cause his or her autism. But this reality will neither stop some people from insisting on a connection when there is none nor will it stop well-meaning parents from deliberately endangering their children's' health.

    Bad Parenting

    Dr. Leo Kanner, the man who first identified autism as a unique condition, had the idea that cold “refrigerator” mothers caused autism. He was wrong.

    But Dr. Kanner's misinterpretation of autism impressed a major figure in psychology, Bruno Bettelheim. Bettelheim's book, The Empty Fortress: Infantile Autism and the Birth of the Self, created a generation of parents who carried guilt for their child's disability. Fortunately, that burden is no longer.

      Factors, Not Causes, Related to Autism

      Some issues seem to have a real connection to autism, though they do not actually cause the condition. In some cases, reducing or addressing the issue may actually reduce some symptoms.

      Immune Deficiency

      There is some evidence that, at least in certain cases, autism is associated with problems in the immune system. Autistic individuals often have other physical issues related to immune deficiency. Some researchers say they have developed effective treatments based on boosting the immune system. The National Institutes of Health (NIH), however, states that the evidence is not yet strong enough to show a causal relationship.

      Food Allergies and Intolerances

      There is also some evidence that children with autism are more prone to gastrointestinal (GI) problems than other children. And there is some evidence to suggest that allergies or intolerances to certain foods may be associated with autistic symptoms.

      Most people who support this theory feel that gluten (a wheat product) and casein (dairy) are the most significant culprits. It's important to note, however, that there is no evidence that food allergies can actually CAUSE autism. Thus, an autistic child with severe gastrointestinal symptoms will behave and learn better if their GI symptoms are treated. But treating GI symptoms will not make autism itself go away.

      Poor Nutrition

      It seems unlikely that malnutrition can cause autism. But megavitamin therapies have been used for years to treat autistic symptoms. Certain supplements—particularly omega fish oils—do seem to be helpful for treating some aspects of autism.

      As children with autism are often very sensitive to tastes and textures, and thus have limited diets, it may be the case that they are lacking specific nutrients important to learning and social/intellectual growth. Again, while improved nutrition may be a helpful therapy, it is not a cure for autism.

      A Word From Verywell

      You'd think that with so much information available, someone could tell you what caused autism in your child. But the odds are you'll never know.

      • Could your individual child have developed autism as a result of heredity?
      • Could he or she have been exposed in utero to something that caused a neurological anomaly
      • Could some post-natal exposure be to blame?

      All possibilities are still under investigation. And it can be very frustrating to live with a disorder—whether as a parent or child—when you know little about its cause.

      The reality, however, is that the vast majority of parents did nothing to cause their child's autism and have no cause for guilt or self-recrimination. While parents may not discover the cause of their child's autism, they can do a great deal to ensure that their child reaches his/her potential and lives the fullest and happiest life possible.


      Caglayan, A. (2010). Genetic causes of syndromic and non-syndromic autism. Developmental Medicine & Child Neurology, 52(2), 130-138. doi:10.1111/j.1469-8749.2009.03523.

      CDC Page on Vaccine Safety

      Exploring Autism

      "Finding Supports Theory That Autism Results From Failure of Brain Areas To Work Together" NIH News, November 2004.

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