President Trump and Health Secretary Robert F. Kennedy Jr. recently released a highly anticipated report on the possible causes of autism, a topic that has long been a focus for both individuals.
Over the past 25 years, autism diagnoses in the United States have significantly increased. Experts attribute this rise, at least in part, to greater public awareness and an evolving definition of the disorder. However, Mr. Trump and Mr. Kennedy have frequently suggested a role for vaccines, a theory that has been disproven by numerous scientific studies.
The new administration report also proposed another potential risk factor: acetaminophen, the active ingredient found in common painkillers like Tylenol, when taken during pregnancy. This potential link has been investigated over the years, but the existing evidence remains inconclusive.
Here’s what scientists currently understand about autism, its potential origins, and associated risks.
What exactly is autism?
Autism spectrum disorder, as it’s formally known, encompasses a wide array of challenges related to social interaction, communication, and repetitive behaviors or thought patterns. The severity of symptoms varies greatly. Some children with an autism diagnosis might only struggle with understanding social cues, while others with more severe cases may face significant impairments, such as difficulty speaking or needing assistance with basic self-care tasks. Currently, autism is diagnosed through observations by clinicians and parental reports, as there are no definitive blood tests or brain scans.
Could genetics be a factor?
While hundreds of genes have been linked to autism, a neurodevelopmental disorder, scientists believe it arises from a complex combination of genetic predispositions and environmental influences.
Helen Tager-Flusberg, a psychologist at Boston University, noted, “Thirty years ago, geneticists were optimistic about identifying perhaps six to ten genes contributing to autism risk. Now, we know that number is literally in the hundreds. Pinpointing the genetic basis of autism is proving to be a far more intricate challenge than initially conceived.”
The Centers for Disease Control and Prevention has conducted extensive research into autism risk factors. Researchers have investigated dozens of potential contributors, including air pollution, exposure to toxic chemicals, and viral infections during pregnancy.
Some studies hint at an elevated risk for babies born to older parents. Other research suggests possible associations with premature birth or low birth weight.
What has research revealed about acetaminophen?
Scientists have been examining acetaminophen, the active ingredient in Tylenol, for over a decade. Some studies involving pregnant women and acetaminophen use have indicated an increased risk of neurodevelopmental disorders in their children later in life. However, other studies that meticulously controlled for confounding factors, including genetics, found no such link.
In August, researchers from the Harvard T.H. Chan School of Public Health and the Icahn School of Medicine at Mount Sinai published a comprehensive review of 46 previous studies on acetaminophen use during pregnancy, with eight specifically focusing on autism.
This review synthesized existing data and did not introduce new findings. While it concluded there was a correlation between acetaminophen use in pregnancy and ADHD and autism, the authors emphasized that this does not prove causation. Women who use Tylenol may differ from those who do not in crucial ways, such as underlying health conditions during pregnancy or their genetic makeup. A significant 2024 study of 2.5 million Swedish children found that the link between acetaminophen use and neurodevelopmental disorders vanished when comparing siblings born to the same mother.
Following the paper’s publication, Dr. Nathaniel DeNicola, an advisor to the American College of Obstetricians and Gynecologists, reiterated that the findings do not alter current medical advice for pregnant patients.
He stated, “The paper concludes that Tylenol should be used cautiously, at the lowest effective dose and least frequent interval. This aligns perfectly with the current standard of care for Tylenol and many other medications, especially during pregnancy.”
What about the vaccine controversy?
The idea that vaccines might cause autism gained traction in the late 1990s after British researcher Andrew Wakefield published a study of 12 children, claiming a link between the measles, mumps, and rubella vaccine and autism.
This theory has been thoroughly debunked over the years by numerous larger-scale studies, including one that encompassed the entire child population of Denmark. Regardless of vaccine types, ingredients, or childhood immunization schedules, researchers have found no connection to autism.
Dr. Wakefield’s 1990 article was retracted in 2010, and he subsequently lost his medical license.
So, why are autism diagnoses increasing so dramatically?
An estimated 1 in 31 U.S. children now have an autism diagnosis, a significant jump from 1 in 150 in 2000. This rise is primarily attributed to a broadening of autism’s definition and diagnostic criteria over several decades.
Autism first appeared in the third edition of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders in 1980.
A 1987 revision expanded the disorder’s definition to include children whose symptoms emerged at later ages, beyond 30 months. The number of diagnostic criteria also increased from six to sixteen, and children only needed to meet half of these new criteria, rather than all six as previously required.
In 1994, the fourth edition of the DSM incorporated Asperger syndrome, characterized by intense focus on a single interest and other traits, into the autism spectrum. This was a pivotal change, allowing individuals with milder impairments and average or even above-average intellectual abilities to receive an autism diagnosis.
The fifth edition of the diagnostic manual, released in 2013, consolidated autism, Asperger syndrome, and PDD-NOS (pervasive developmental disorder-not otherwise specified) into a single diagnosis: autism spectrum disorder. It also enabled clinicians to provide a combined diagnosis of autism spectrum disorder and attention deficit hyperactivity disorder.
Data from the Centers for Disease Control and Prevention indicates that while the prevalence of profound autism (defined by intellectual disability and severe language impairments) slightly increased from 2000 to 2016, other autism diagnoses rose much more sharply.
Increased public awareness has also significantly contributed to the rising diagnoses. The widespread availability of special services in schools, beginning in the 1990s, incentivized parents to seek diagnoses for their children. Furthermore, pediatrician recommendations for universal screening of infants at 18- and 24-month well-child visits have ensured earlier detection.
Researchers also highlight the growing online discourse about autism as a recent factor. Videos on TikTok and YouTube discussing autism have garnered billions of views, and online communities like Reddit have provided platforms for individuals to find connection and identity.
“Is there room also for there being an actual increase beyond those variables? I would say probably yes, because some of the things that are associated with autism, the nongenetic factors, those are also changing,” Dr. Tager-Flusberg noted.
“Over time we have come to the understanding that the biology of this disorder is far more complex than we might have ever imagined.”