What the Experts (Not the Politicians) Have to Say About the Rise and the Causes of Autism Spectrum Disorders

Autism spectrum disorders (ASD) are some of the most talked-about developmental conditions of our time. If you’ve followed the headlines, you’ve probably noticed dramatic claims about an “autism epidemic,” worries about environmental toxins, pseudoscience about vaccines, pain killers and passionate debates about what autism actually is.

One of the most worrisome aspects of this ongoing debate is the fact that similar to the debate about the value of vaccinations, COVID treatments, and about science in general, it has become politized with the loudest voices coming from politicians without any scientific background.

Beneath the noise, though, science has been steadily painting a more complex picture, one that blends genetics, biology, environment, and society in ways that defy easy answers.

The Numbers: Why Are Autism Diagnoses Rising?

Over the past two decades, reported cases of autism have risen steeply. In the United States, estimates of prevalence went from 1 in 150 children in 2000 to 1 in 31 by 2022. Similar increases have been noted in the UK, Scandinavia, South Korea, and Japan.

At first glance, this looks alarming, as though autism itself is spreading like an epidemic. Some people have included ASD in the group of chronic conditions, making up the current non-contagious disease epidemic. But researchers stress that what we’re really seeing is not necessarily a sudden surge in “true” autism, but rather a shift in how the condition is defined, detected, and understood.

Changing Diagnostic Rules

Until the 1990s, autism was defined narrowly in medical manuals. A child had to meet strict criteria, and diagnoses were largely limited to young children with very obvious symptoms. That changed when the DSM-IV (1994) and ICD-10 (1990) broadened the definitions. Later, the DSM-5 (2013) merged separate categories like Asperger’s syndrome into a single umbrella: autism spectrum disorder. These updates meant that many more children, and adults, now fit these much broader diagnostic criteria.

Growing Awareness

Teachers, doctors, and parents have become much more familiar with autism. Where once a child might have been labeled “difficult” or “socially awkward,” today that same child might be assessed and diagnosed with ASD. Girls and women, long overlooked, are increasingly recognized as autistic. Adults, too, are seeking diagnoses after struggling for years without an explanation.

Earlier Detection

Children are being assessed at younger ages, thanks to better screening tools and rising awareness in schools and clinics. This not only boosts numbers, but also helps families access support earlier in life.

Based on these considerations, most scientists agree that the majority of the dramatic increase in prevalence reflects better detection, broader definitions, and reduced stigma, not a sudden explosion of autism prevalence itself.

How Common Is Autism?

Different ways of counting give different answers. The CDC’s Autism and Developmental Disabilities Monitoring Network (which tracks school and health records) reported the often quoted “1 in 31” figure among 8-year-olds in 2022. But such registry studies may over- or undercount cases depending on how diagnoses are recorded.

A more rigorous approach is to directly screen populations. The Global Burden of Disease study estimated that about 1 in 127 people worldwide (less than 1%) are autistic, amounting to 62 million people in 2021. In contrast, some surveys in Japan and other countries have found higher rates, up to 3% in certain groups of children.

This wide range suggests that while autism is indeed common, and rates may indeed have been continuously increasing, exact prevalence depends heavily on how and where you look.

What Causes Autism?

This is perhaps the most pressing and controversial question, and the answer is complicated. Researchers agree on one thing: there is no single cause for this development disease. Autism arises from an interplay of genetics and early environment, with genetics carrying the heavier weight.

Genetics: The Largest Piece of the Puzzle

Family studies show that autism tends to run in families. Large international research projects estimate that about 80% of autism risk comes from genetics, a level of heritability much higher than for obesity and metabolic disorders, but comparable to height.

But the genetic picture is intricate. Some cases can be traced to rare but powerful mutations in certain genes, which may appear for the first time in a child (so-called de novo mutations). These explain autism in perhaps 10–20% of cases. More commonly, autism arises from the accumulation of many small genetic variations, each with a tiny effect, but together enough to tip the balance.

Environmental Influences: A Smaller But Real Role

Despite the powerful genetic influences, many experts have emphasized that these genetic risk factors have always been there, so the more recent increase in clinical cases must be due to some changing environmental factors during the past century. Genes don’t act in isolation. A handful of environmental exposures have been linked to increased risk, mostly before birth. Examples include:

• Parental age: Older mothers and fathers are more likely to have children with autism, perhaps because of an increased chance of genetic mutations in eggs or sperm.
• Pregnancy factors: Infections during pregnancy, complications, or exposure to certain pollutants may modestly increase risk. Preclinical studies have shown that maternal immune activation results in neurodevelopment abnormalities, presenting with autism-like behavior. Studies in large databases suggested an increase in ASD cases in mothers who had the flu during pregnancy. However, the findings were not conclusive, and arguing against this role of maternal immune activation is the fact that no significant increase in ASD prevalence has occurred during the COVID pandemic.
• Alterations in the gut microbiome and in brain-gut microbiome interactions.
• Air pollution: Several studies suggest that exposure to fine particulate matter or other pollutants during pregnancy may play a role.

It’s important to stress that these risks are probabilistic, not deterministic, they slightly increase the odds, but do not cause autism outright.

One of the most damaging misconceptions about ASD causes have been the claim that vaccines cause autism. Multiple large studies have thoroughly disproven any link between vaccines and ASD. The theory propagated by Andrew Wakefield, which falsely linked the measles, mumps, and rubella (MMR) vaccine to autism, was exposed as a fraudulent and unethical hoax and Wakefield was stripped of his medical license.

The vast majority of healthcare professionals agree that vaccines remain safe and vital for public health. The recent pseudoscientific warnings from the highest level of the U.S. Government that Tylenol taken by pregnant mothers increases the risk of ASD in the offspring is another myth that only contributes to the confusion of mothers with an autistic child.

Living with ASD

While debates about causes often dominate headlines, autistic individuals and their families emphasize that understanding prevalence and biology is only part of the picture. Just as crucial are support, acceptance, and recognition of the diversity within autism.

Autism is a spectrum. Some autistic people live independently and thrive in work and relationships, while others need lifelong support. Many have co-occurring conditions like high disease-related anxiety leading to digestive symptoms, increased sensory perception, ADHD, epilepsy, or intellectual disability.
Statements that devalue autistic people, such as claims they can’t work or contribute to society, are harmful and inaccurate. Many autistic adults are employed, pay taxes, and lead meaningful lives. Advocacy groups stress that research should not only search for causes but also focus on improving services, education, and inclusion.

Why the Debate Matters

Public discussion around autism is often politically charged. For example, U.S. Health and Human Services Secretary, Robert F. Kennedy Jr. recently called autism an “epidemic” caused by an environmental toxin and promised new research to find the culprit. Many scientists and autism advocates criticized this framing, warning that it oversimplifies decades of research and risks reviving debunked theories about vaccines.

What the science shows instead is that autism’s rise in reported cases reflects changing definitions, awareness, and detection, and that its causes are largely genetic, with some environmental contributions occurring in utero. There is no “silver bullet” explanation.

The science of autism is still evolving. Future research will likely uncover more about how specific genes interact with each other and which prenatal influences play a significant role in individuals with genetic risk factors. By slashing or redirecting research funding and wasting resources to pursue debunked concepts with federally funded research studies will not accelerate the development of effective therapies.

This post was inspired by the recent political debates about causes of the increase in ASD cases articles in the lay press and by a News Feature article published in Nature 644, 860-863 (2025); doi: https://doi.org/10.1038/d41586-025-02636-1