The number of autism cases has multiplied in recent years. Why is this?

Robert F. Kennedy Jr. spoke of an "alarming increase" when he presented the latest figures on the prevalence of autism to the media in mid-April: In the United States, approximately 3 percent of children are diagnosed with autism today, compared to 0.04 percent in the 1980s. Later in the press conference, Kennedy, the new U.S. Secretary of Health and Human Services, described autism as an "epidemic" and pledged to identify the "environmental toxins" responsible for the developmental disorder by September.

Kennedy plans to commission a whole series of studies to investigate whether food additives, pesticides, or ultrasound examinations can cause autism. The long-dismissed hypothesis that vaccinations are a possible trigger will also be reexamined.

The number of autism diagnoses has increased not only in the USA. The phenomenon is occurring worldwide. In England, there has been an increase of almost 800 percent in twenty years, and in Germany , the number has doubled in the past ten years. There is no data available on the situation in Switzerland. However, experts and institutions see the same trend there as well. For example, the membership of the non-profit organization "Autism Switzerland" has increased fivefold since 2013.

How do experts explain the increase in cases? And what is already known about the causes of autism?

Peter Vermeulen, one of Belgium's leading autism experts, believes it's wrong to call it an epidemic. "The situation isn't comparable to an infectious disease triggered by a pathogen," says the special education teacher. "There's no single cause of autism." Rather, he believes it's a complex interplay of genetic predispositions and environmental influences.

Kennedy, known as a conspiracy theorist, suspects the measles vaccine as one of these influences. Vermeulen strongly contradicts this: The accusation that the vaccine causes autism dates back to a falsified study from the 1990s that has long since been retracted. Several studies have since ruled out a connection between the measles vaccine and autism. In Japan, for example, the number of autism cases continued to rise even after the vaccine was no longer used there.

According to Vermeulen, the timing of the diagnosis can also lead to false suspicion of vaccination. In autistic children, it's often around 18 months of age that it's first noticed that they interact with their environment differently than their peers. It's precisely during this phase of life that many vaccinations are administered. "But these children were already autistic," says Vermeulen. "Because the causes are largely genetic."

Studies have shown that genetic factors account for 80 to 90 percent of the development of autism. If one identical twin is autistic, the other usually is as well. However, this doesn't mean that there are individual autism genes. Rather, the developmental disorder is based on a vast number of different genes.

"The genetics behind each case are unique," explains Helene Haker, a Zurich-based psychiatrist specializing in autism. The mutations can be compared to grains of sand: "If enough of them are in unfavorable places in the system, a disorder can develop."

Some environmental influences are also already known. A fever-associated infection in pregnant women during the second trimester increases the likelihood of having an autistic child. Gestational diabetes , certain epilepsy medications , and air pollution are also considered risk factors. However, none of these are likely to have been the main cause of the massive increase in autism cases in recent years.

Part of the increase can be explained by the fact that people in industrialized countries are becoming parents later and later in life. The risk of giving birth to an autistic child increases with each year of the father's and mother's lifespan.

Above all, however, most experts are convinced that the increase in diagnoses is due to increased sensitivity to the disorder and changing definitions. Psychiatrist Ludger Tebartz van Elst from the University Hospital Freiburg im Breisgau shares this view. "I notice this in myself," he says. "Today, I diagnose people as autistic whom I would have given no diagnosis or a different diagnosis twenty years ago." This is increasingly the case with women.

At the turn of the millennium, autism was still believed to be primarily prevalent in boys and men. It was even referred to as an extreme form of the male brain. Today, it's undisputed that there are also many autistic women. However, autistic girls and women often make great efforts to adapt and hide their differences. To do so, they imitate the behavior of non-autistic people. Experts like Tebartz van Elst are now more likely to recognize such cases. "We're simply more attentive," he says.

What's more, diagnostic criteria have changed considerably since the 1980s. The two internationally recognized manuals for the classification of mental disorders, the DSM and the ICD, have repeatedly adjusted their definitions of autism.

Forty years ago, the focus was primarily on early childhood autism, which was often accompanied by intellectual disability. In the 1990s, the diagnosis of Asperger's syndrome was introduced: Those affected exhibit difficulties in social interaction and a stereotypical repertoire of interests, but their intelligence is usually normal. For about ten years now, these categories have been combined with atypical autism to form the autism spectrum disorder, which can take very different forms. It is said that every autistic person is different .

The impact of the changed criteria on the number of cases has been documented by several studies: Among other things, a Danish study from 2015 showed that 60 percent of the increase in autism diagnoses in children was due to changes in the diagnostic criteria and a stronger clinical focus on autism.

The societal perception of autism has changed. Today, more people know what autism is. The stigma has diminished, the diagnosis has become more attractive, and even mild cases are being investigated.

"That's all good," says psychiatrist Helene Haker. But some developments go too far for her. "While my colleagues previously hardly dared to make the diagnosis, some have now developed tunnel vision for it," she says. Other diagnoses, such as personality disorders or post-traumatic stress disorders, which could explain similar conditions, are thus ignored.

According to Haker, young people who struggle to find their way in the world due to such disorders prefer innate neurodiversity as an explanation, even if they are not autistic according to the classical definition. "These people then seek out one specialist after another until they receive their diagnosis," explains the psychiatrist.

Special education teacher Peter Vermeulen observes a similar situation. "Autism is still partly underdiagnosed today, but often also overdiagnosed," he says. Vermeulen also sees a reason for this in influencers on Instagram and TikTok, who call themselves experts but convey a one-sided view of autism.

Too often, the focus there is on autistic people who have few difficulties in society. "You know, we're not 'Rain Man,'" he hears repeatedly on social media. But people like Raymond from the film "Rain Man," whose everyday lives are severely limited by autism, do exist, says Vermeulen.

"More research is needed, especially for these people," he says. According to Vermeulen, it would be helpful to find out how such autistic people can better cope in life. How they can find jobs and integrate into society. These are the studies that Robert F. Kennedy Jr. really needs to initiate, he says.