Last Modified: February 16, 2023 | Published: February 2, 2023

Autism has become increasingly prevalent. Public awareness in America has now increased to the point that it is now common to bump into someone with autism among friends and relatives.  

There is a recent debate over whether autism is a disease, disorder, or simply a set of personal traits. Questions abound regarding the causes of this complex set of symptoms. An ASD diagnosis can have great meaning within a person’s identity, and it also can be the cause of significant distress for a family. For some, autism is simply one small aspect of a person’s myriad of traits. For others, autism brings a lot of pain due to increased difficulties in forming connected relationships.

A precise cause of autism is unknown. However, there is emerging research indicating many potential causes. Here are some of the leading causes to date.

Genetic causes of autism  

The primary cause of autism is genetics. We know that autism has a strong genetic component.  Autism can pass from generation to generation.  It may skip a generation passing from grandparent to grandchild. The ‘autism gene’ is highly complex. 

Autism involves over 100 different potential gene combinations and mutations. Inheriting autism is not as clear-cut as eye color. Heritability rates have been identified, ranging from 36-95% (Greening, 2020). However, recent estimates hover around a heritability of about .8.  This heritability means that 80% of cases where a cause can be identified are traceable to a genetic or inherited cause (Bai et al., 2019). 

Genes and environment in autism 

The genetic cause is only half the story. The vast majority of autism research points to the combination of genes and environment. It is possible that certain children are particularly fragile or susceptible to autism symptoms.  The environment may influence gene expression. 

Early brain development is most likely when these genes and environmental factors collide to have the most influence (Miani et al., 2021). This begins to explain how there are certain areas of the country where autism is much more prevalent than others. Although the genes are there, pregnant mothers who are exposed to certain toxins may be more likely to have a child with autism symptoms. Taken together, genetics are the primary cause of autism, but environmental factors appear to play a significant role in the expression of symptoms.

Epigenetics in autism: a combination of genes and environment over generations 

The genetics of autism is highly complex and is made even more interesting by the study of epigenetics.  This is the study of how environmental influences can cause changes in presentation even when genes stay the same. Many different factors can have an impact. Factors including maternal in-utero habits or conditions play a role in symptom expression. For example, obesity, smoking, hunger, and alcohol use, can increase autism risk. Without changing genes, the expression of certain characteristics can change in certain environments (Oztenekecioglu et al., 2021).

 For example, environmental toxins like pesticides and herbicides show a potential link to autism. These chemicals are noted to be an emerging risk factor. In countries where those pesticides are disallowed, the rates of autism can be lower. However, even in countries like the United States, where these pesticides are regularly used, most people won’t get autism. Rather, autism seems to develop after certain in-utero or breast milk exposures to toxins in babies who are medically fragile or predisposed to the disorder (He et al., 2022). 

“Pregnancy seems to be the time when pesticide exposure appears to have the greatest impact on the onset of ASD in children” (Miani et al., 2021). This is an example of one way epigenetics may play a role in autism. There could be a myriad of other environmental conditions that contribute to gene expression in autism. Although scientists diligently search for the precise contributing factors, research continues to conclude that autism comes from a combination of genes and environment. 

Parental age: older age increases autism risk 

Parental age is a factor in developing autism. Bear in mind that older parental age contributes to the risk of many developmental disabilities. This is not a unique issue in autism. While most may assume that the mother’s age is the primary issue, the father’s age is a major contributor to autism risk. Age can lead to changes in sperm methylation.  

This may be an intergenerational risk factor, meaning that a son who was born to an older father may have an increased risk of having a child with autism (Bolte, Girdler & Marschik, 2019). Several research studies exist investigating the link between fathers who have children later in life and autism (Bolte, Girdler & Marschik, 2019; Hultman et al., 2011).

Sometimes knowing risk factors can help a family get a jump start on treatment.  We know that early treatment and early intervention lead to the healthiest brain development and best outcomes.

Vaccines: a mythical cause of autism 

The myth that vaccines cause autism has been continually debunked. The research is overwhelmingly clear. For the purpose of this article, it will be helpful for parents to know some of the major findings that refute the vaccine argument (see also Kroncke et al., 2016). 

1) The authors of the original study linking autism to vaccines had a sample size of fewer than 20 individuals and was later found to be fraudulent. 

2) A later study including hundreds of thousands of individuals showed that there was no correlation between vaccinations and autism.

3) After fears spread in the US, almost 10% fewer parents chose to vaccinate their children, and the rates of autism continued to steadily rise.

 4) Finally, the ingredient that was accused of causing autism was removed from common childhood vaccinations. The result? Autism rates continued to rise. (Kroncke et al., 2016)

Kids with a genetic disposition toward developmental disabilities are more sensitive to various illnesses. These children require greater protection in the form of vaccines than the general population. Taken together, vaccines don’t cause or prevent autism. They could prevent other serious medical issues.

It is important for families to know the following about autism causes. First, autism prevalence is truly on the rise. It is not a simple reclassification of other disorders or an issue with diagnostic clarity. Autism is caused by some combination of genetics and environmental factors. At this time, it appears that in utero or early life exposures to toxins are the biggest risk factors. Autism can present with some unique and important personal traits that are to be valued and treasured in our diverse society. It can also bring many challenges for a family. The best way to find out whether or not autism is the cause of some of your child’s symptoms is to get a comprehensive assessment.

How do you get an autism assessment?

Unfortunately, the process of getting an autism evaluation is not easy. For many families, it takes many months, or even years, to get in for an assessment. Learn more in this blog article about what a comprehensive evaluation looks like. See this course for information about autism signs.

References: autism research 

Bai D, Yip BHK, Windham GC, et al. Association of Genetic and Environmental Factors With Autism in a 5-Country Cohort. JAMA Psychiatry. 2019;76(10):1035–1043. doi:10.1001/jamapsychiatry.2019.1411

Bölte, S., Girdler, S., & Marschik, P. B. (2019). The contribution of environmental exposure to the etiology of autism spectrum disorder. Cellular and Molecular Life Sciences, 76(7), 1275-1297.

Greening, N. K. (2020). Foundations in Autism Spectrum Disorders and Related Neurodevelopmental Disorders: Possible Causes, Characteristics, Diagnosis, and Treatment. Advances in Social Sciences Research Journal, 7(7) 293-318.

He, X., Tu, Y., Song, Y., Yang, G., & You, M. (2022). The relationship between pesticide exposure during critical neurodevelopment and autism spectrum disorder: A narrative review. Environmental Research, 203, 111902.

Hultman, C. M., Sandin, S., Levine, S. Z., Lichtenstein, P., & Reichenberg, A. (2011). Advancing paternal age and risk of autism: new evidence from a population-based study and a meta-analysis of epidemiological studies. Molecular psychiatry, 16(12), 1203-1212.

Kroncke, Anna P., & Willard, Marcy & Huckabee, Helena (2016). Assessment of autism spectrum disorder: Critical issues in clinical forensic and school settings. Springer, San Francisco.



Miani A, Imbriani G, De Filippis G, De Giorgi D, Peccarisi L, Colangelo M, Pulimeno M, Castellone MD, Nicolardi G, Logroscino G, Piscitelli P. Autism Spectrum Disorder and Prenatal or Early Life Exposure to Pesticides: A Short Review. International Journal of Environmental Research and Public Health. 2021; 18(20):10991.

Ongono, J. S., Béranger, R., Baghdadli, A., & Mortamais, M. (2020). Pesticides used in Europe and autism spectrum disorder risk: can novel exposure hypotheses be formulated beyond organophosphates, organochlorines, pyrethroids and carbamates?-A systematic review. Environmental research, 187, 109646.

Oztenekecioglu, B., Mavis, M., Osum, M., & Kalkan, R. (2021). Genetic and epigenetic alterations in autism spectrum disorder. Global Medical Genetics, 8(04), 144-148.