# What Causes Autism? What the Evidence Actually Says > A clear, evidence-based answer to what causes autism — the role of genetics and brain development, what's still unknown, and the myths to ignore (including vaccines). _Source: Autism Parent Guide (https://autismparentguide.org/autism/causes) · Last reviewed 2026-06-01 · Reviewed by Parent reviewer and Developmental paediatrics adviser._ ## Quick answer There is no single cause of autism. The evidence points strongly to **genetics and early brain development** — autism tends to run in families and is shaped by the way the brain develops, mostly before birth. It is **not caused by parenting, by anything you did or didn't do, by screen time, or by vaccines** — the vaccine link has been thoroughly disproven. For most children, autism comes from a complex mix of inherited factors, and often no specific cause is ever identified. That's normal, and it's not your fault. ## If you're blaming yourself — please don't Many parents quietly worry they caused their child's autism. **You did not.** Autism is not caused by parenting style, by working, by vaccines, by the food you ate in pregnancy, or by giving your child a screen. Carrying guilt helps no one — your energy is far better spent understanding and supporting your child. If guilt or low mood is weighing on you, talk to your doctor; looking after yourself is part of looking after your child. ## What parents can do today - Let go of self-blame — the science is clear that this is not your fault. - Be cautious of websites or sellers offering to "reverse" or "cure" autism, especially for a fee. - If you'd like, ask your paediatrician whether genetic testing is appropriate — it's optional and a personal choice. - Focus your energy on understanding and supporting your individual child today. ## Genetics: the strongest factor Research consistently shows autism is largely *heritable* — it runs in families. Studies of twins and families find that when one identical twin is autistic, the other very often is too. Hundreds of different genes have been linked to autism, which is part of why it looks so different from child to child. For most children there isn't one "autism gene" to point to. Instead, many small genetic factors combine. Sometimes autism is linked to a specific genetic condition (such as Fragile X syndrome or tuberous sclerosis), and a doctor may discuss genetic testing — but for the majority of children, no single genetic cause is found, and that's completely normal. ## Early brain development Autism is connected to differences in how the brain develops and forms connections, mostly very early — often before a baby is born. This is why signs can appear so young and why autism is lifelong. These are *differences* in development, not damage, and not something caused by how a child is raised. ## Other factors that may play a small part Alongside genetics, researchers have studied a number of factors that may slightly raise the likelihood of autism. These don't *cause* autism on their own, and most children with these factors are not autistic: - Being born very prematurely or at a very low birth weight - Older parental age - Certain conditions or medications during pregnancy (always discuss medication with your doctor — never stop prescribed medicine on your own) - Having a sibling who is autistic These are associations seen across large groups of people, not predictions about any one child. ## What does NOT cause autism Some ideas have been studied carefully and **firmly ruled out**. These do not cause autism: - **Vaccines, including the MMR vaccine.** The original claim was based on fraudulent, withdrawn research, and many large, high-quality studies since have found no link. Vaccines protect your child from serious illness. - **Parenting.** The old "cold parent" theory was wrong and has been completely rejected. Love, warmth and parenting style do not cause autism. - **Screen time, sugar, or diet.** These don't cause autism. - **Anything you did during pregnancy out of normal life.** Be especially wary of products, diets, supplements or clinics that promise to *cure* or *reverse* autism. Some are expensive, and a few are genuinely unsafe. ## Why "why" matters less than "what now" It's natural to want a reason. But for most families, there is no clear single cause to find — and knowing the cause usually wouldn't change the support a child needs anyway. Once the search for blame is set down, parents often feel freed up to focus on what genuinely helps: understanding their child, supporting communication, and building a calmer, more predictable day. If you'd like a practical next step, see [what to do if you're worried](/diagnosis/first-steps) or explore the free [Parent Toolkit](/toolkit). ## Frequently asked questions ### Do vaccines cause autism? No. This has been studied repeatedly in very large groups of children, and there is no link between vaccines (including MMR) and autism. The original study claiming a link was found to be fraudulent and was retracted. Vaccinating protects your child. ### Is autism genetic or inherited? Autism is strongly genetic and tends to run in families, though usually no single gene is responsible. It often comes from many genetic factors combining. Sometimes it's linked to a specific genetic condition, which is why a doctor might offer genetic testing. ### Did something I do in pregnancy cause my child's autism? Almost certainly not. Autism is mainly shaped by genetics and early brain development. Normal life during pregnancy does not cause autism. If you took prescribed medication, discuss it with your doctor for reassurance — but never stop prescribed medicine on your own. ### Can autism be caused by trauma or parenting? No. Parenting style, working, daycare, and screen time do not cause autism. The old idea that distant parenting caused autism has been completely disproven. ### Should my child have genetic testing? It's optional and a personal decision. Genetic testing sometimes identifies a related condition, which can occasionally guide medical care, but it usually doesn't change day-to-day support. Your paediatrician can talk you through whether it's worth it for your family. ## Sources - Causes of autism / what causes autism — NHS - Autism spectrum disorder — risk factors and causes — CDC - Vaccine safety and autism research summaries — American Academy of Pediatrics (AAP) --- **Not medical advice.** This information is general and educational. Always speak to a qualified professional about your individual child. Free parent tools: build printable communication cards at https://autismparentguide.org/toolkit/cards