When U.S. presidential candidate Robert F. Kennedy Jr. recently claimed that autism rates are skyrocketing due to “environmental toxins” and dismissed genetic causes, he reignited one of the most persistent and controversial public health debates of the last 30 years. But autism researchers and medical professionals say those assertions are not supported by science.
The increase in autism diagnoses, they argue, reflects expanded diagnostic criteria, earlier and broader screening, and increased public awareness — not a sudden spike in the condition itself, and certainly not one caused by vaccines or environmental exposure alone.
“There’s no credible evidence that toxins or vaccines are driving autism rates,” said Dr. Alycia Halladay, chief science officer at the Autism Science Foundation. “The real story is how we’ve become better at identifying autism, especially in children who would have been missed a generation ago.”
Diagnoses Are Increasing — But Understanding Has Changed
According to the U.S. Centers for Disease Control and Prevention (CDC), one in 36 children in the United States is now diagnosed with autism spectrum disorder (ASD), a sharp rise from one in 150 in the year 2000. While that number may appear alarming, experts caution against misinterpreting it as a surge in the actual number of people with autism.
“Changes in diagnostic criteria, not environmental factors, are responsible for most of the increase,” said Dr. Catherine Lord, a clinical psychologist and professor at UCLA. “We’re seeing more children diagnosed because the medical system is finally reaching them.”
In recent decades, autism has been defined more broadly to include a wider range of neurodevelopmental conditions. Children who might once have been labeled as having a developmental delay, speech impairment, or learning disability are now more accurately recognized as being on the autism spectrum.
This diagnostic evolution — known as “diagnostic substitution” — is widely acknowledged in peer-reviewed research as a major driver of increased prevalence.
The Vaccine and Toxin Debate: A Discredited Theory Persists
Despite numerous studies debunking any link between vaccines and autism, Kennedy and others continue to suggest a connection — often citing thimerosal, a mercury-based preservative that was removed from most childhood vaccines by 2001.
However, autism diagnoses continued to rise even after thimerosal’s removal, a fact public health agencies highlight as further disproof of the alleged connection. Large-scale studies, including those published by the Institute of Medicine, the World Health Organization, and the CDC, have consistently shown no link between vaccines and autism.
“Vaccines have become a scapegoat,” said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia. “But the data are clear. Vaccines do not cause autism, and suggesting otherwise only spreads fear.”
Similarly, studies on environmental toxins like air pollution, pesticides, and plastics have produced inconclusive and inconsistent findings. While some exposures during pregnancy may marginally increase risk, scientists emphasize these are not dominant factors.
The Genetic Foundation of Autism
Recent genetic studies have underscored the powerful role heredity plays in autism. Twin studies estimate that between 74 and 93 percent of autism risk is attributable to genetic factors — a figure that dwarfs any potential environmental contributors.
“Autism is one of the most heritable neurodevelopmental disorders we know,” said Dr. Joseph Buxbaum, director of the Seaver Autism Center at Mount Sinai. “Environmental factors might modulate risk slightly, but they don’t explain the rise in diagnoses. Genetics does.”
Experts say that blaming toxins or vaccines undermines scientific progress and can steer families away from seeking real support for their children.
Global Perspective: Increased Recognition, Not Epidemic
The World Health Organization estimates that about 1 in 100 people globally are autistic. In many low- and middle-income countries, the rate may be lower — not because fewer people are autistic, but because of underreporting, stigma, or limited access to diagnostic services.
“What we’re really seeing is not an autism epidemic,” said Dr. Halladay. “We’re seeing a recognition epidemic.”
Indeed, as more healthcare systems embrace early childhood screening, more cases are being caught — particularly among children from historically underserved communities.
As public debate continues to swirl, experts stress the need to rely on evidence-based understanding — not outdated fears — in shaping public health policies and attitudes toward autism.