What Is Autism? A Clear Guide for Parents

What is autism? Autism is a lifelong difference in how the brain develops. It affects how a person communicates, relates to others, and experiences the world, and it often comes with focused interests, a strong need for routine, and sensory differences. Autism is not an illness or the result of parenting, and every autistic child is different [1][2].

What is autism, in plain words?

When parents ask “what is autism?”, the simplest answer is this. Autism, or autism spectrum disorder (ASD) as doctors write it, describes a brain that develops and works differently from most people’s. The difference is present from early childhood, even if it is not noticed until later [3]. It is called a “spectrum” because it looks very different from one person to the next.

Some autistic children talk early and love facts about trains or planets. Others speak few or no words and communicate in other ways, such as gestures, pictures, or devices. Some have an intellectual disability and some do not. In US surveillance data, about 4 in 10 autistic eight-year-olds with available test scores also had an intellectual disability [4].

Another way to answer what is autism comes from autistic people themselves. Many families and autistic adults see autism as part of who a person is, not something to be “fixed.” This neurodiversity view sits alongside medical care: it asks that support focuses on a child’s wellbeing, communication, and independence rather than making them look less autistic [5]. People also differ in the words they prefer. Some say “autistic child,” and others say “child with autism” [6]. Both are used on this site.

What is autism to a doctor? The two core areas

Doctors in the US use the DSM-5-TR (the American Psychiatric Association manual, 2022), and the UK and many other countries use the World Health Organization’s ICD-11. Both describe autism using the same two core areas [7][3].

1. Social communication and interaction

• Less back-and-forth sharing, such as pointing to show you something or bringing toys to show you.
• Differences in eye contact, facial expressions, and gestures.
• Finding it hard to join in play, make friends, or understand unwritten social rules.

2. Restricted or repetitive behaviors, interests, or senses

• Repetitive movements, such as hand-flapping, rocking, or spinning (often called stimming).
• Strong need for sameness, and distress at small changes.
• Very intense or unusual interests, or lining up and sorting objects.
• Being over- or under-sensitive to sounds, lights, textures, smells, tastes, or pain.

These features must start in early development and must make everyday life harder for a diagnosis to be made. ICD-11 also notes that some autistic people cope in many settings through great effort, so their difficulties may not be obvious to others, and a diagnosis can still be right for them [3]. You can read more in our guide to the DSM-5-TR autism criteria.

How common is autism?

The CDC’s Autism and Developmental Disabilities Monitoring Network found that about 1 in 31 eight-year-olds (3.2%) at 16 US sites had been identified as autistic in 2022. Boys were identified about 3.4 times more often than girls [4]. A global review estimated a median of about 1 in 100 children worldwide, with big differences between countries that partly reflect how much screening and diagnosis is available [8].

Numbers have risen over time. The American Academy of Pediatrics (AAP) explains that this rise is linked to more awareness, more screening, earlier identification, and a broader definition of autism, which now includes children who were once given other labels or none at all [9]. Girls may still be missed more often than boys; see our guide to autism in girls.

What is autism caused by?

There is no single cause. Twin and family studies show that genes explain most of the variation in who is autistic, with heritability estimated at around 80% in a study of two million people across five countries [10]. Hundreds of genes are involved, and in some children a specific genetic change or condition (such as fragile X syndrome) is found [1].

Some factors around pregnancy and birth, such as being born very early or having older parents, are linked to a somewhat higher chance of autism, but most of these effects are small [11]. Large, high-quality studies have found again and again that vaccines do not cause autism [12][13]. Parenting style does not cause autism either.

Autism and other conditions

Autistic children are more likely than other children to have certain additional health or developmental conditions. The AAP lists sleep problems, feeding difficulties, gut symptoms such as constipation, seizures, ADHD, and anxiety among the common ones [1]. A large review found that mental health conditions such as anxiety and ADHD are much more common in autistic people than in the general population [14].

These conditions matter because they can be treated or supported, and they can make daily life much harder if missed. A sudden change in behavior, sleep, or eating is always worth discussing with your child’s doctor, because pain or illness can be hard for some autistic children to describe.

How is autism identified?

There is no blood test or brain scan for autism. Diagnosis is based on a careful developmental history from parents and a trained professional’s observation of the child [15]. The AAP recommends that all children are screened for autism at their 18- and 24-month checkups, as well as having their development checked at every visit [1].

The AAP notes that autism can be diagnosed as young as 18 months of age [1], and a large study found that diagnoses made from about 14 months onward were usually stable over time [16]. Yet in the US the median age of earliest known diagnosis was 47 months in the 2022 data [4]. Our guide to early signs of autism in toddlers walks through what to look for.

What you can do at home

Knowing what is autism, and what it is not, helps you notice your child’s needs and strengths. These steps help whether or not your child is autistic.

• Watch and note. Write down what you see: how your child asks for things, plays, reacts to sounds, and copes with change. Short videos on your phone can help a doctor understand.
• Use free milestone checklists. The CDC’s “Learn the Signs. Act Early.” milestones show what most children do by each age [17].
• Follow your child’s lead in play. Join in with what they enjoy. This builds connection and communication, whatever the outcome of any assessment [18].
• Keep routines predictable. Many autistic children feel calmer when they know what comes next. Simple picture schedules can help.
• Look after yourself, too. Learning about autism takes time. Connect with trusted sources and other parents.

When to talk to a professional

Talk to your child’s doctor if you notice signs of autism, if your child is not meeting milestones, or if they lose words or skills they had before. Loss of skills at any age should be checked promptly [17][19]. You do not need a diagnosis to ask for help. In the US, children under 3 can be referred to their state’s early intervention program by a parent or doctor, and services can start before any diagnosis [20]. In the UK, start with your GP or health visitor [21].

Frequently asked questions

Is autism a disease?

No. Autism is a neurodevelopmental difference, meaning the brain develops in a different way from early life. It is not an infection or an illness that can be caught or passed on by contact. The NHS describes it as a difference in how the brain develops rather than an illness. Some autistic people need a lot of support, and many also have other health conditions that do need treatment.

Can autism be cured?

There is no cure for autism, and claims that a product or treatment can cure it are not supported by evidence. What helps is the right support: communication help, adapting the environment, understanding at home and school, and treating any other health problems such as poor sleep, anxiety, or constipation. Many autistic children make strong progress over time with this kind of support.

Is autism caused by bad parenting?

No. Old theories blaming parents were wrong and have been abandoned. Research shows that genes play the largest known role, along with some factors before or around birth. Nothing you did, or did not do, as a loving parent caused your child to be autistic. Your involvement and understanding can, however, make a real difference to how supported your child feels.

What age can autism be diagnosed?

Experienced clinicians can often diagnose autism reliably at around 2 years of age, and sometimes earlier. The AAP recommends autism screening for all children at 18 and 24 months. However, many children, especially girls and children with strong language skills, are not identified until school age or later. A diagnosis can be made at any age if the signs are there.

References

1. Hyman SL, Levy SE, Myers SM; Council on Children With Disabilities, Section on Developmental and Behavioral Pediatrics. Identification, Evaluation, and Management of Children With Autism Spectrum Disorder. Pediatrics. 2020;145(1):e20193447. Link
2. NHS. What is autism? Page last reviewed 6 May 2026. Link
3. World Health Organization. Clinical descriptions and diagnostic requirements for ICD-11 mental, behavioural and neurodevelopmental disorders (CDDR). Geneva: WHO; 2024. ISBN 9789240077263. Section 6A02 Autism spectrum disorder. Link
4. Shaw KA, Williams S, Patrick ME, Valencia-Prado M, Durkin MS, Howerton EM, et al. Prevalence and Early Identification of Autism Spectrum Disorder Among Children Aged 4 and 8 Years – Autism and Developmental Disabilities Monitoring Network, 16 Sites, United States, 2022. MMWR Surveill Summ. 2025;74(2):1-22. Link
5. Pellicano E, den Houting J. Annual Research Review: Shifting from ‘normal science’ to neurodiversity in autism science. J Child Psychol Psychiatry. 2022;63(4):381-396. Link
6. Kenny L, Hattersley C, Molins B, Buckley C, Povey C, Pellicano E. Which terms should be used to describe autism? Perspectives from the UK autism community. Autism. 2016;20(4):442-462. Link
7. American Psychiatric Association. DSM-5-TR Fact Sheet: Autism Spectrum Disorder. Washington, DC: APA; 2022. Link
8. Zeidan J, Fombonne E, Scorah J, Ibrahim A, Durkin MS, Saxena S, et al. Global prevalence of autism: A systematic review update. Autism Res. 2022;15(5):778-790. Link
9. American Academy of Pediatrics Council on Children With Disabilities Autism Subcommittee. Understanding Autism: Information for Families. HealthyChildren.org. Last updated February 20, 2026. Link
10. Bai D, Yip BHK, Windham GC, Sourander A, Francis R, Yoffe R, et al. Association of Genetic and Environmental Factors With Autism in a 5-Country Cohort. JAMA Psychiatry. 2019;76(10):1035-1043. Link
11. Modabbernia A, Velthorst E, Reichenberg A. Environmental risk factors for autism: an evidence-based review of systematic reviews and meta-analyses. Mol Autism. 2017;8:13. Link
12. Hviid A, Hansen JV, Frisch M, Melbye M. Measles, Mumps, Rubella Vaccination and Autism: A Nationwide Cohort Study. Ann Intern Med. 2019;170(8):513-520. Link
13. American Academy of Pediatrics Section on Infectious Diseases. Vaccine Safety: Examine the Evidence. HealthyChildren.org. Last updated April 3, 2026. Link
14. Lai MC, Kassee C, Besney R, Bonato S, Hull L, Mandy W, et al. Prevalence of co-occurring mental health diagnoses in the autism population: a systematic review and meta-analysis. Lancet Psychiatry. 2019;6(10):819-829. Link
15. Centers for Disease Control and Prevention. Clinical Testing and Diagnosis for Autism Spectrum Disorder. Last reviewed May 8, 2025. Link
16. Pierce K, Gazestani VH, Bacon E, Barnes CC, Cha D, Nalabolu S, et al. Evaluation of the Diagnostic Stability of the Early Autism Spectrum Disorder Phenotype in the General Population Starting at 12 Months. JAMA Pediatr. 2019;173(6):578-587. Link
17. Centers for Disease Control and Prevention, Learn the Signs. Act Early. CDC’s Developmental Milestones. Last reviewed February 17, 2026. Link
18. American Academy of Pediatrics Council on Children With Disabilities Autism Subcommittee. If Autism is Suspected, What’s Next? HealthyChildren.org. Last updated April 3, 2025. Link
19. National Institute for Health and Care Excellence. Autism spectrum disorder in under 19s: recognition, referral and diagnosis. Clinical guideline CG128. Published 28 September 2011; last updated 20 December 2017 (minor changes 2021-2025). Link
20. American Academy of Pediatrics. What is Early Intervention? HealthyChildren.org. Last updated December 23, 2025. Link
21. NHS. Autism assessments. Page last reviewed 6 May 2026. Link

This guide is general education, not medical advice. Always talk to your child’s doctor or care team. Last checked: October 2026.