Are more children developing autism, or are doctors diagnosing it differently?

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The statistics are staggering: In the 1960s and ‘70s, autism was considered a rare condition. Early epidemiological studies suggested that about two to four children per 10,000 were autistic. By 2000, when the U.S. Centers for Disease Control and Prevention launched its nationwide surveillance program, the agency reported that about 1 in 150 American children had autism. 

Today, that number has risen to 1 in 31, or roughly 322 cases per 10,000 children — about 100 times greater than estimates from 50 years ago.

The dramatic increase has fueled one of the most contentious disputes in medicine and public health: Is autism actually becoming more common, or are clinicians simply becoming better at recognizing it? 

Amy Lutz has spent decades trying to unravel that question — for her 27-year-old son with profound autism, and for the scientific community at large. 

“There’s a huge debate raging in the autism community about whether prevalence is actually increasing or whether these dramatically rising rates are an artifact of more awareness or expanded diagnostic categories or other, more social factors,” said Lutz, a senior lecturer in the History and Sociology of Science department at the University of Pennsylvania. 

Scientists are still piecing together a complete understanding of autism and the factors that contribute to it. While researchers have identified hundreds of genes associated with the condition and uncovered important clues about prenatal development, they still cannot fully explain why autism diagnoses have grown so dramatically over half a century. That uncertainty has left room for competing theories — and fierce disagreement — over what the numbers really mean. 

Diagnoses are rising. But what does that mean?

Every two years, the CDC’s Autism and Developmental Disabilities Monitoring Network estimates how many children meet the criteria for autism spectrum disorder by reviewing health and educational records. Those reports have documented a huge uptick: The prevalence of autism among 8-year-olds has risen nearly fivefold in the past two decades. 

But those reports are often misunderstood, said Joseph Buxbaum, director of Mount Sinai’s Seaver Autism Center for Research and Treatment. 

“The surveillance mechanism is in place to raise questions,” he explained. “Surveillance mechanisms say something is happening. They don’t say we understand all of this.” 

The CDC’s surveillance data doesn’t provide any clues as to why autism is becoming more common.

One reason, Buxbaum argues, is that the definition of autism itself has changed.

Brianna Soukup/Portland Press Herald via Getty Images.

When the condition was first described in 1943, autism was generally reserved for children with profound communication impairments and significant intellectual disabilities, he said.

In the past few decades, diagnostic criteria broadened and routine developmental screening became more common. In 2013, the Diagnostic and Statistical Manual of Mental Disorders consolidated several previously separate diagnoses under the umbrella of autism spectrum disorder. These included Asperger syndrome and “pervasive developmental disorder not otherwise specified” —  a category for people with autistic features who did not fit neatly into the existing diagnoses.

Those changes dramatically expanded who could receive an autism diagnosis, and some researchers and autism advocates say that has artificially inflated the sense of a burgeoning autism epidemic. 

“I’m pretty sure there’s no true biological increase in prevalence,” said Buxbaum, who is also a professor of psychiatry, neuroscience and genetics at the Icahn School of Medicine. 

He points to studies that have revisited historical medical records and others that have evaluated older adults using today’s diagnostic criteria. Those studies consistently find autism prevalence close to 1% across generations — suggesting many people who would be diagnosed today simply went unrecognized decades ago.

Diagnosis itself has also become more valuable.

For many families, a diagnosis is a gateway to specialized educational services, behavioral therapies, insurance coverage and other support that may not otherwise be available. Adults also increasingly seek evaluations, hoping to better understand lifelong social or communication challenges.

“Older adults find it helpful to have a diagnosis because it gives them some insight into themselves,” Buxbaum said. 

At the same time, society’s acceptance of autism has changed profoundly. Once a highly stigmatized diagnosis, autism has become far more widely recognized and understood. 

“I will say that I think our awareness campaigns have A: Done a terrific job. And, B: Perhaps done too terrific a job,” said Helen Tager-Flusberg, the former director of Boston University’s Center for Autism Research Excellence.

“Everyone became aware of autism and it developed a kind of a cachet. So people who were having social issues, social problems, all of a sudden, you’re on the spectrum,” said Tager-Flusberg, now a professor emerita at Boston University. “And then these days, of course, they’ll go to social media and they’ll watch some TikTok reels and all of a sudden there’s a lot of self-diagnosis going on. So things just kind of blossomed in that way.”

The conversation around autism has shifted so dramatically that, in some circles, a diagnosis that many once sought to hide has become part of a person’s identity.

“I can’t believe I’ve lived to see this, but autism has become trendy. It’s become something that’s self-diagnosed that people celebrate as an identity,” Lutz said.

Taken together, broader diagnostic criteria, increased awareness, reduced stigma, earlier screening and greater access to services provide one explanation for why diagnoses have skyrocketed — even if the underlying prevalence of autism has barely changed. 

Others are not convinced.

Could some of the increase be real?

“What’s very bizarre to me is we have absolute Mount Everest mountains of data showing these colossal, stupendous, astronomical increases in autism, and we don’t have, counterbalancing that, data that actually shows that it’s from these alleged sources,” like earlier screenings or reduced stigma, said Jill Escher, the president of the National Council on Severe Autism. 

Changes in diagnosis have become the default explanation for rising autism prevalence, despite what Escher sees as insufficient evidence.

Some researchers believe that at least part of the increase may reflect a genuine rise in autism incidence. 

“Do more people today have autism than they did 30 years ago? I think the answer is probably yes because some of the prenatal risk factors we know are increasing,” Tager-Flusberg said. 

One of those factors is parental age. 

“We know that increased parental age is a significant risk factor for autism,” she said. “Older parents are more likely to have a child with autism.”

The average age of first-time mothers has risen from 21.4 years old in 1970 to 27.5 today. The share of babies born to mothers younger than 30 fell from roughly 70% in 1990 to fewer than half by 2023. Over the same period, the share of babies born to mothers 35 and older more than doubled — from 7.6% to 16.8% — while births to mothers 40 and older more than tripled, from 1.2% to 4.1%, according to the CDC.

“In and of itself,” Tager-Flusberg said, “that would lead to an increase in the actual numbers of autism.”

Tager-Flusberg pointed to rising rates of maternal obesity and related medical conditions, which have been linked to an increased risk of autism. Researchers are also investigating whether exposure to plastics, for instance, may interact with underlying genetic susceptibility. Because it is notoriously difficult to pinpoint which factors might impact health, evidence of many of those exposures is less certain. 

Autism isn’t the only condition becoming more common

Just as autism diagnoses are booming, rates of attention-deficit/hyperactivity disorder (ADHD) have risen in recent years alongside broader screening and evolving diagnostic criteria. And Alzheimer’s disease is being diagnosed at significantly higher rates as physicians have improved their ability to recognize the disease and distinguish it from other forms of dementia.

Today’s debates on autism remind Buxbaum of ones he heard earlier in his career, while studying Alzheimer’s disease.

“There was never any Alzheimer’s when I was a kid,” people told him then. “It’s got to be something in the cans. It’s something in the pots.”

Today, the sharp rise in autism diagnoses has inspired similar speculation. President Donald Trump and Health and Human Services Secretary Robert F. Kennedy Jr. have repeatedly suggested that environmental factors are driving the increase. They point to potential culprits ranging from acetaminophen, the active ingredient in Tylenol, to food additives and other chemical exposures.

“We know it’s an environmental exposure. It has to be,” Kennedy said at a press conference last year. “Genes do not cause epidemics. They can provide a vulnerability, but you need an environmental toxin.”

Scientists agree that environmental factors likely contribute to autism risk in at least some children. The question is which ones, how impactful they are and how they interact with a person’s underlying genetics. While some prenatal risk factors — such as older parental age and exposure to certain medications during pregnancy — are supported by substantial evidence, many other proposed explanations, including Tylenol and plastics, remain under active investigation or lack conclusive evidence. 

Before Alzheimer’s disease was widely recognized and clinically defined, many older adults with dementia were simply described as “senile,” Buxbaum said. For years, a definitive diagnosis often could not be made until after death, when brain tissue could be examined.

“As we understood the different kinds of dementia, we no longer used a catch-all term,” Buxbaum said. “The rates haven’t changed a bit.”

Autism, he said, has undergone a similar evolution.

Decades ago, children who might have been diagnosed with intellectual disability, developmental delay or another neurodevelopmental disorder may today be diagnosed with autism. Researchers call this diagnostic substitution.

A 2009 study estimated that shifting diagnoses from intellectual disability to autism in California explained about a quarter of the increase in autism cases between 1992 and 2005. 

But national CDC data is less clear. Between 2019 and 2020, parent-reported diagnoses of autism, intellectual disability and other developmental disorders all increased, suggesting that autism’s rise cannot fully be explained by children simply moving from one diagnostic category to another. 

Is America facing an autism crisis?

Decades of rising diagnoses, alarming headlines and high-profile claims by Trump and Kennedy have left many Americans with the impression that the country is in the midst of an autism epidemic. While there is little debate that the number of children and adults diagnosed with autism has increased dramatically, the debate over what is causing this increase is massive. 

Are today’s numbers primarily the result of a wider diagnosis funnel thanks to broader diagnostic criteria, greater awareness and reduced stigma? Or do they also reflect a genuine increase in autism, fueled in part by changing prenatal risk factors or other environmental exposures that scientists are still working to understand? 

Researchers say one of the biggest barriers to answering that question is that autism itself is extraordinarily complex. Rather than a single disorder with a single cause, evidence increasingly suggests autism arises through many different biological pathways involving genetics, prenatal development and environmental influences that likely vary from person to person.

Scientists have made enormous progress over the past two decades, identifying hundreds of autism-related genes and several established prenatal risk factors. But understanding how those pieces fit together — and how much each contributes to autism’s rising prevalence — has proven far more difficult. 

The next generation of scientific inquiry could finally begin to answer those questions. As scientists follow families before and during pregnancy while tracking genetics, maternal health and environmental exposures over time, they hope to better distinguish which risk factors contribute to autism and which are simply associated with it.

The answer could impact future research, as well as where society invests its resources — whether expanding lifelong services for a growing autistic population, identifying preventable risk factors or, most likely, both.

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