During his confirmation hearings two weeks ago to lead the Department of Health & Human Services (HHS), Robert F. Kennedy Jr. repeated several unfounded claims about autism.

Kennedy, an environmental lawyer who has made money through books, speeches and lawsuits while sharing vaccine skepticism, refused to say that vaccines don’t cause autism despite many high-quality studies finding no such link.

He stated during the hearing that autism rates have “have gone from 1 in 10,000 … and today in our children, it’s one in 34.” His claims have been repeated by President Donald Trump on Truth Social.

It’s unclear where Kennedy got his 1 in 10,000 statistic. In 2000, approximately 1 in 150 children in the U.S. born in 1992 were diagnosed with autism compared with 2020, during which one in 36 children born in 2012 were diagnosed, according to data from the Centers for Disease Control and Prevention.

Some psychiatrists and autism experts told ABC News it’s important to highlight the rising rates of autism, and that at least Kennedy is putting a spotlight on it.

“On the bright side, I think it is really important to place an emphasis on these very high rates, it’s kind of great putting a spotlight on autism, these increased rates,” Dr. Karen Pierce, a professor in the department of neurosciences at the University of California, San Diego and co-director of the UCSD Autism Center of Excellence, told ABC News. “We need more funding. We need more infrastructure to support everybody who is now recognized as on the spectrum. So, I think that that’s actually a really good thing.”

However, the experts said Kennedy and others are missing important context about why autism rates are increasing. They say reasons may include a combination of widening of the definition of the spectrum and of types of symptoms associated with autism spectrum disorder (ASD) as well as people having children at older ages, better awareness and access to diagnostic testing.

“With the rates increasing, there certainly are valid reasons for that,” Pierce said. “There’s better awareness, and doctors can find autism a lot easier than they could before in the past…. and I think a very big reason is just better record keeping nowadays and easier access to reviewing records.”

What is autism?

ASD is a developmental disability caused by differences in the brain, according to the CDC.

People with ASD often communicate, interact, behave and learn differently, the CDC says. ASD symptoms typically begin before age 3 and can last a lifetime, although symptoms may change over time.

“There can be differences in how one is reading social cues and interpreting them, and then there’s also certain behaviors that we see,” Dr. Anna Krasno, clinical director of the Koegel Autism Center at the University of California, Santa Barbara, told ABC News.

“So those include a preference for sameness, a difficulty with transitioning, some cognitive and behavioral rigidity,” she continued. “We also see intense interests, so topics that people are super, super into and want to research, repetitive speech and motor movements. And then we also see really significant sensory differences as well.”

ASD is a spectrum, which means symptoms vary by person — some need little support in their daily lives and some may need a great deal of support in performing day-to-day activities. Some may have advanced conversation skills and others may be nonverbal.

Wider recognition, better understanding

Experts told ABC News there is a wider recognition and a better understanding of what is now understood as autism/ASD.

In the early 1900s, autism was described as a symptom of the most severe cases of schizophrenia, and it was considered a psychiatric disorder for many years.

Traits of what is now known as ASD are built on early observations in the 1940s from Austrian-American psychiatrist Dr. Leo Kanner and Austrian physician Dr. Hans Asperger.

A 1943 paper from Kanner described 11 children who presented with “inborn autistic disturbances of affective contact” while Asperger’s 1944 report focused on boys who had marked social difficulties; unusual, circumscribed interests; and good verbal skills.

It was not until 1978 that autism was recognized as a developmental disorder distinct from schizophrenia by the World Health Organization. It was also in the 1970s that psychologists and psychiatrists first came to describe autism as a spectrum.

“When autism was first described, it was new to people understanding that there was a condition that included social communication difficulties and restricted and repetitive behavior, and people primarily only recognized it when it was at its most extreme,” Dr. Jeremy Veenstra-VanderWeele, division director in child and adolescent psychiatry at Columbia University, told ABC News.

“And so, if you go back and read the initial descriptions today, those are kids who we would recognize in the waiting room, recognize in the grocery store, in whom autism would be very obvious and would not require much assessment in order to diagnose,” he continued.

Better diagnostic tools

Experts say another reason for the increase in rates is having better diagnostic tools than what was available decades ago.

There is no single tool used as the basis of an ASD diagnosis. Typically, tools rely on descriptions from parents or caregivers of a child’s development and a professional’s observation of a child’s behavior, according to the CDC.

Currently, the Autism Society encourages all children to be screened for signs of autism by their family pediatrician three times by the age of three — at nine, 18, and 24 or 30 months. If a child shows symptoms of ASD, more rigorous diagnostic testing can be carried out by a specialist including a full neuropsychological exam.

Additionally, the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) provides standard criteria for helping diagnose autism.

Under DSM-5, a child meets the criteria if they have deficits in three areas of social communication and interaction and at least two of four types of restricted, repetitive behaviors.

While the first edition of DSM came out in 1952, it was not until the third edition, DSM-3, in which autism was listed under an entirely new “class” of conditions — the Pervasive Developmental Disorders.

Veenstra-VanderWeele said the change in the criteria is another reason why the number of those diagnosed with autism rose. He likened it to changing the definition of what it means to be tall.

“To just use a crude example, if you would define somebody as tall if they were over six-foot-six, and then 30 years later, say that somebody is tall if they’re over five-foot-10, you’d get very, very different numbers, and that’s part of what’s happened here,” he said.

Pierce added that because of limited knowledge and awareness in the past, there may have been many children who were underdiagnosed and misdiagnosed.

“It’s understandable that people wouldn’t even necessarily think that somebody has autism, because nobody knew what really autism was,” she said. “So, you know, large numbers of people were just put in the books as just having special education needs, maybe as a language delay or of having a cognitive impairment.”

Older reproductive age

Some studies have suggested that people who become pregnant at an older age have an increased risk of giving birth to a child with autism.

A 2012 review and meta-analysis of 16 papers from researchers in New York, London, Israel and Sweden found an association between advanced maternal age and the risk of autism.

Advanced paternal age may also be a risk factor. A 2006 study conducted jointly by researchers in New York, London and Israel found that men who were above age 40 were 5.75 times more likely to have a child with ASD compared to men younger than age 30 after controlling for other factors.

However, questions still swirl about whether or not there is a risk from the age of parents, and not all researchers are convinced.

“I know that there is some research looking at maternal and paternal age with regard to autism, and there’s research around environmental causes,” Krasno said. “I think where I always firmly land is that it is inherited, and it is genetic. So, I don’t know the exact correlation between age and diagnostic rate, but we do know that genetics are highly associated with diagnosis.”

Environmental risk factors

Researchers are also divided over whether or not environmental risk factors play a role in causing autism.

The National Institute of Environmental Health Sciences says the “clearest evidence” involves events before and during birth, including prenatal exposure to air pollution or pesticides; maternal obesity or diabetes; extreme prematurity; and periods of oxygen deprivation to the brain during birth.

“But these factors alone are unlikely to cause autism. Rather, they appear to increase a child’s likelihood for developing autism when combined with genetic factors,” NIEHS states on its website.

Pierce said from the studies she’s read, evidence suggests autism is a genetic condition. She added the environmental factors may play a role but “to a small degree.”

Myth that vaccines cause autism

The myth that vaccines cause autism was born out of a fraudulent 1998 study, hypothesizing that the measles, mumps, rubella vaccine caused intestinal inflammation, which, in turn, led to the development of autism.

The paper has since been discredited by health experts, retracted from the journal in which it was published, and its primary author, Andrew Wakefield, lost his medical license after an investigation found he had acted “dishonestly and irresponsibly” in conducting his research.

More than a dozen high-quality studies have since found no evidence of a link between childhood vaccines and autism.

However, Kennedy has held fast to this claim, saying during a 2023 interview on Fox News that he believes autism comes from vaccines.

During the HHS confirmation hearings, Kennedy said he was not “anti-vaccine” but “pro-safety.” At the same time, Kennedy repeatedly refused throughout the hearings to say that vaccines were not linked to autism, while still insisting he supports vaccination in general.

Experts told ABC News there is no evidence to suggest a link between vaccines and autism, and perpetuating the myth can be dangerous.

“Once there’s a lie and it’s spread, it doesn’t matter that it’s a lie. Once people hear it, then they believe that it’s true despite all of the Herculean efforts to disprove it and debunk it,” Pierce said. “There’s no evidence for it whatsoever, and there’s actually extremely, as far as scientific evidence is concerned, there’s extremely strong evidence to suggest absolutely not.”

Christopher Banks, president and CEO of the Autism Society of America, said the false claim that vaccines cause autism can divert financial resources from much-needed research.

“Instead of advancing support and therapies, time and funding are wasted disproving a debunked theory,” he said. “This misinformation also fuels stigma, implying that autism is something to be feared rather than understood and supported, leading to discrimination against autistic individuals.”

ABC News’ Dr. Jade Cobern, Cheyenne Haslett and Will McDuffie contributed to this report.