On September 22, 2025, former President Donald Trump made headlines by advising pregnant women to avoid Tylenol (acetaminophen), suggesting a possible link between the medication and autism in children. He also claimed that certain communities with limited access to Tylenol—such as the Amish—”don’t have autism,” sparking renewed public debate. His remarks added fuel to a long-standing question that many families still grapple with: what causes autism? Are medications like Tylenol truly part of the equation, or does the scientific evidence point in another direction? Let’s explore what the research actually says.

Autism affects 1 in 36 children in the United States today, yet its causes remain one of medicine’s most fascinating puzzles. For decades, families and researchers have sought answers to this fundamental question. The good news? Science has made remarkable progress in understanding this complex condition.

Here’s what we know: autism isn’t caused by one single factor. Instead, it’s the result of a complex dance between our genes and the environment around us. Let’s break down the science in a way that makes sense.

It’s in the Genes (Mostly)

The strongest evidence points to genetics as the primary driver of autism. Twin studies tell us this story clearly: if one identical twin has autism, there’s a 60% chance the other will too [1]. Compare that to non-identical twins, where the rate drops significantly. Scientists estimate that genetics account for up to 80% of autism risk [2].

But here’s where it gets interesting – there’s no single “autism gene.” Instead, researchers have identified hundreds of genes that can contribute to autism. Some are inherited from parents, while others are brand-new mutations that occur spontaneously. These de novo mutations happen for several reasons: as we age, our reproductive cells accumulate more DNA copying errors, environmental exposures can damage genetic material, and sometimes it’s just the natural imperfection of cell division. Think of it like a complex recipe where many different ingredients can affect the final outcome.

Some of these genes help brain cells find their proper place during development, like RELN, which acts like a GPS system for neurons. Others, like MeCP2, work as master switches that control when other genes turn on or off – when this gene doesn’t work properly, it can cause developmental differences that affect communication and behavior. Then there are genes like NLGN3 and NLGN4 that help brain cells talk to each other, particularly affecting how we understand social cues and connect with others.

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Environmental Influences: The Plot Thickens

While genes set the stage, environmental factors can influence whether autism develops. These factors don’t cause autism by themselves, but they can increase the risk in genetically susceptible individuals.

The most consistent finding involves paternal age. Fathers over 35 have a higher chance of having a child with autism [3]. Why? Older sperm is more likely to carry new genetic mutations.

Pregnancy factors also matter. Maternal infections, diabetes, high blood pressure, and certain medications (particularly valproic acid, used for seizures) have all been linked to increased autism risk [3]. Birth complications like premature delivery or low birth weight also play a role.

The Brain Connection: Where It All Comes Together

So how do genes and environment create the autism we recognize? The answer lies in how the brain develops and connects with itself.

A groundbreaking 2024 study from Yale University gave us our clearest picture yet [4]. For the first time, researchers measured brain connections in living autistic adults. They found something remarkable: autistic brains have 17% fewer synapses – the connections between brain cells that allow communication.

Think of synapses like the intersections in a city’s road network. Fewer intersections mean information travels differently through the brain. The study also found that people with fewer synapses showed more pronounced autism characteristics.

This supports what scientists call the “pruning theory.” During early development, our brains create way more connections than we need – imagine a garden that grows wildly before being carefully trimmed. Then, through a process called synaptic pruning, we eliminate the weaker or less-used connections to make our brains more efficient. In autism, this pruning process appears to work differently – sometimes too much pruning occurs, sometimes too little, and sometimes it happens at the wrong time. This creates a unique pattern of brain connectivity that can lead to both the challenges and remarkable abilities we see in autism [5].

This different wiring helps explain many autism characteristics. It can lead to heightened sensitivity to sounds or textures, challenges with social communication, and the intense focus that many autistic people experience.

The Gene-Environment Dance

Here’s where epigenetics comes in – the study of how genes get turned on and off. Environmental factors during pregnancy can essentially flip genetic switches, changing how brain development unfolds without altering the DNA itself [3].

Imagine genes as a piano and environmental factors as the pianist. The same piano can produce vastly different music depending on which keys are pressed and when. This explains why autism is so diverse and why genetic risk doesn’t always lead to autism.

Debunking the Myths

Let’s be crystal clear about what doesn’t cause autism:

Vaccines do not cause autism. This concern arose from a 1998 study that suggested a possible link, but this research had serious methodological problems and was later retracted by the medical journal that published it. Since then, numerous large-scale studies involving millions of children worldwide have consistently found no association between vaccines and autism. The scientific consensus is clear: vaccines are safe and do not increase autism risk.

Tylenol (acetaminophen) does not cause autism. Some studies have suggested a possible association between prenatal acetaminophen use and autism, but these studies show correlation, not causation. This could be explained by reverse causation – perhaps mothers who later have autistic children experience more stress, infections, or other conditions during pregnancy that require pain relief, rather than the medication itself causing autism. Many factors could explain these findings, and major medical organizations maintain that acetaminophen remains safe when used as directed during pregnancy.

How parents raise their children doesn’t cause autism. In the 1950s, some people wrongly believed that distant or emotionally cold mothers caused autism in their children. This hurtful idea was proven wrong decades ago and caused unnecessary guilt for countless families. We now know that autism is a neurological condition present from birth, not something caused by parenting.

The Bigger Picture

Understanding autism’s causes isn’t just academic – it’s deeply practical. This knowledge helps us:

• Identify children who might benefit from early intervention
• Develop better support strategies
• Reduce stigma through scientific understanding
• Guide families making reproductive decisions

The autism puzzle is complex, but each piece of research brings us closer to the full picture. We now know that autism results from the intricate interplay between genetic predisposition and environmental influences, leading to a uniquely wired brain that processes the world differently.

Rather than seeing autism as something that needs to be “fixed,” this understanding helps us appreciate the neurological diversity that makes each autistic person unique. The goal isn’t to eliminate autism, but to better support autistic individuals so they can thrive in a world designed for neurotypical brains.

Science continues to unlock autism’s mysteries, promising not just better understanding and acceptance, but also more precise and effective interventions tailored to each person’s unique neurological profile.

Frequently Asked Questions (FAQ) about Autism Causes

1- Is autism caused by bad parenting?

A: Absolutely not. We now know that autism is a neurological condition and is not caused by how a person is raised.

2- Can you “get” autism later in life?

No, autism is a developmental condition that begins before birth, though it may not be diagnosed until later in childhood or even adulthood.

3- Is there a single cause of autism?

No, there is no single cause. Autism is a complex condition caused by a combination of genetic and environmental factors.

4- What is the main cause of autism?

Genetics is the main cause, accounting for up to 80% of the risk. However, it is not one gene but a combination of many genes interacting with environmental factors.

References

[1] Rylaarsdam, L., & Guemez-Gamboa, A. (2019). Genetic Causes and Modifiers of Autism Spectrum Disorder. Frontiers in Cellular Neuroscience, 13. https://pmc.ncbi.nlm.nih.gov/articles/PMC6710438/

[2] UCLA Health. (2024). Is Autism Genetic? https://medschool.ucla.edu/news-article/is-autism-genetic

[3] Karimi, P., Kamali, E., Mousavi, S. M., & Karahmadi, M. (2017). Environmental factors influencing the risk of autism. Journal of Research in Medical Sciences, 22. https://pmc.ncbi.nlm.nih.gov/articles/PMC5377970/

[4] Yale School of Medicine. (2024). A Key Brain Difference Linked to Autism Is Found for the First Time in Living People. https://medicine.yale.edu/news-article/a-key-brain-difference-linked-to-autism-is-found-for-the-first-time-in-living-people/

[5] Columbia University Irving Medical Center. (2014). Children with Autism Have Extra Synapses in Brain. https://www.cuimc.columbia.edu/news/children-autism-have-extra-synapses-brain