Understanding What Causes Autism Today.

1. A Clinician’s Perspective

I’m drawing on over 25 years of clinical experience diagnosing and supporting individuals with autism to explain what modern research/science tells us about the causes of autism, what myths persist, and why diagnoses have become more common. The article combines research findings with practical guidance for families seeking accurate information and early support. For this article, I will use autism and Autism Spectrum Disorder (ASD) interchangeably.

2. How Understanding of Autism Has Evolved

Autism is not something caused by parenting or environmental exposure alone; it reflects neurodevelopmental differences affecting social communication, sensory processing, and behavior.

In 2013 all of the neurodevelopment conditions in the Pervasive Developmental Disabilities (Autistic Disorder, Asperger’s Disorder, PDD-NOS, etc.) were merged into Autism Spectrum Disorder (ASD) in the DSM-5 (2013). This change was made because the American Psychiatric Association’s committee on Pervasive Developmental Disabilities suggested current research supported such a consolidation to improve consistency and access to services.

Currently, there are no medical tests that accurately identify or diagnosis ASD (i.e., blood tests, genetic test, or other medical procedures). The diagnosis of an Autism Spectrum Disorder (ASD) relies on behavioral observation and clinical evaluation.

To access medically needed therapy like Applied Behavioral Analysis (ABA), Speech Language Therapy (SLP), Occupational Therapy (OT), or other allied health services, a family will need to get an evaluation by a medical provider (i.e., psychologist, pediatrician, neurologist or multidisciplinary team), but most diagnostsis are provided by clinical psychologists that specialize in the diagnosis of ASD. Typically commercial health insurance or Medicaid will pay for these evaluations.

In contract, for your child to receive special education services through your local school district, families will need to ask their school for a Educational Team Determination (EDT) to determine if your child meets the criteria for special education services. Following the EDT, the educational team will complete an Individualized Educational Plan (IEP) to identify which special education services your child receives. School districts will provide these services at no costs to you.

Earlier and more consistent screening tools now allow to identify infants who are at-risk for ASD as early at 8-months and some young children can show sufficient behaviors to diagnose ASD as early as 12 months. The best thing you can do is ask for a screening for autism as soon as you have your first concern vs waiting to see if they grow out of it.

3. What the Science Says About Causes

Genetic Factors

• Genetics account for roughly 80–90% of overall autism risk.
• Risk comes from both rare, high-impact gene variants and many small common variants that act together (polygenic risk) to produce autism symptoms, developmental delays, and severity of symptoms.
• A 2025 international study confirmed that genetic combinations also help explain differences in severity, language ability, and cognition across the spectrum.

The takeaway:

• Autism looks different from person to person because their genetic mix is unique,
• If there is a close relative who has ASD and your child is showing developmental delay, then you want to seek an autism screening or full evaluation,
• Autism is primarily caused by genetic factors and are not caused by vaccines, parenting style, or Tylenol.

Environmental and Perinatal Factors

“Environmental” means influences that impact an individual’s development outside of the direct impact of their DNA.

Factors with the most consistent evidence that can increase the risk of a future ASD diagnosis include:

• Parental age (older maternal and paternal age slightly increases risk).
• Valproate (Depakote) use during pregnancy (~3x increased risk).
• Very preterm birth or very low birth weight.
• Serious maternal infections (e.g., congenital rubella).
• Some studies show small risk increases for air pollution or pesticides, but these effects are modest.

Overall: genetics drive most risk, with small additive contributions from prenatal factors.

4. Known Risk Factors with Practical Numbers

• Sibling recurrence: ~22–26% risk for younger siblings of autistic children.
• Advanced parental age (older than 40 years of age at conception): ~18–21% increase risk per decade.
• Valproate exposure: ~4.4% absolute risk.
• Very preterm birth: consistently higher odds of ASD.

These are the most reliable figures families can use in discussions with their child’s primary care physician and share with the psychologist conducting your child ASD evaluation.

5. What Is Not a Cause

• Vaccines (including MMR): Proven not to cause autism; the 1998 paper linking them was retracted.
• Tylenol/acetaminophen during pregnancy: Evidence does not support a causal link; professional guidelines consider it safe when needed.
• Parenting style: There is no evidence to indicate your parenting style contributes to the diagnosis of ASD. Even those children who experience extreme abuse or neglect do not experience a higher rate of ASD.

These myths persist because simple stories spread faster than complex science.

6. The Importance of Early Screening

• The American Academy of Pediatrics recommends screening at 18 and 24 months.
• Families with an older autistic child should screen even earlier (10–12 months).
• Telehealth screenings can be highly effective, allowing clinicians to observe a child’s natural behavior at home.
• Early screening leads to earlier access to intervention, which is strongly linked to better developmental outcomes.

If you’d like to discuss early screening or evaluation options for your family, talk with our Care Team to explore your next step.

7. Why Autism Diagnoses Have Increased

Based on 30 decades of research, prevalence monitoring, and clinical experience, the increase in autism prevalence is due to a variety of changes in societal acceptance, diagnostic criteria, screening/surveillance procedures, and increased access. Here are some specific examples of why autism rates have increased over the past 30 years:

• DSM-5 combined several categories into one spectrum.
• Routine pediatric screening.
• Earlier identification in childhood.
• Greater public awareness.
• Insurance coverage for services.
• Diagnostic reclassification in schools.
• More clinicians and diagnostic programs.
• Better identification among girls and minority groups.
• Telehealth and remote evaluations.
• Expanded CDC surveillance.

Together, these factors explain the increase in autism rates without invoking any new environmental cause.

8. Where Our Focus Should Be

I urges that while research into genetics and biology should continue, the greater priority is supporting individuals across the life span who are living with autism today. I’m concerned the Federal funding cuts of 2025 to healthcare, education, and research will adversely impact this primary goal without ongoing advocacy by all of us. Here are some specific areas of advocacy you can invest your time and energy to make a significant impact for our community:

• Full funding for early childhood and special education.
• Broader access to evidence-based behavioral interventions.
• Practical community supports (communication tools, vocational training, sensory-friendly environments, and housing).
• Recognition that behavioral and educational interventions, not medications, are the most effective ways to improve quality of life.

9. Final Guidance for Families

Parents concerned about their child’s early developmental need to pursue an early screening and diagnostic evaluation. This is especially true if your child has an immediate relative that has been diagnosed with an Autism Spectrum Disorder (ASD).

If you have concerns, don’t wait. A brief conversation with our Care Team can help you understand what a comprehensive diagnostic evaluation looks like and whether it’s the right next step for your family.