Autism Spectrum Disorder (ASD)

Autism is a difference in the way the brain develops, and it shapes how a person communicates, thinks and takes in the world. The World Health Organisation describes autism as a diverse group of conditions.¹

Autism is not an illness, and there is no cure for it.² Support is available; it works on the specific difficulties a person has.

What autism is, and what it is not

Autism is a neurodevelopmental difference: the word means the difference arises as the brain develops, very early in life. It is present from birth and stays with a person for life, and the NHS describes it as a difference in how the brain develops.²

People often speak of autism as neurodivergence rather than as a condition to be corrected; neurodivergence means a brain that works differently from the common pattern.

Autism is not a mental illness, and therapy does not treat it.²

Autistic people may live with anxiety, depression or other difficulties alongside autism, and those can be treated in their own right.

Abilities and needs vary between autistic people, and they change over time.¹ Some autistic people live independently and others need substantial support throughout life. The diagnostic criteria reflect this. They rate severity as a level of support needed, running from requiring support, to substantial support, to very substantial support.⁷

The criteria state explicitly that the severity levels do not correspond to whether a person qualifies for or needs services. They take no account of an individual's profile of abilities, or of their own order of priorities.⁷

A note on language

There are two ways of writing about autism: identity-first language says autistic person, and person-first language says person with autism. This page uses identity-first language, because many autistic adults prefer it, while clinicians often default to person-first wording.³

A survey of the UK autism community found no single term that everyone accepts, and some of that disagreement is strong.⁴ Ask the person which they prefer, then use it.³

How autism shows up

Autism affects social communication and interaction. The descriptions that follow draw on NHS guidance for autistic adults, and children may present differently. Reading facial expressions, gestures or tone of voice can be hard work. Language may be taken literally, so hints and figures of speech are easy to miss.⁵

Light, sound, smell, taste or texture may feel far more intense than expected. They may also barely register at all.⁵

An autistic adult may have fixed ways of doing things, and changes to routine can be distressing. Repetitive movement is often called stimming. Rocking, hand flapping and finger flicking are common examples.⁵

An autistic adult may also be very focused on specialist interests.⁵ These are not a symptom to be discouraged. WHO names a focus on detail among the patterns it describes.¹

Masking is the effort of covering all of this in order to fit in. It can leave ordinary social contact exhausting and stressful.⁵

The diagnostic criteria acknowledge masking directly. They note that autistic characteristics may not become fully apparent until social demands exceed a person's capacities. Learned strategies may mask them in later life.⁷ That is part of why a person can reach adulthood undiagnosed.

How common autism is

The World Health Organisation estimates that about 1 in 127 people had autism in 2021.¹ That figure is an average, not a headcount. Reported rates vary substantially between studies, and across many low and middle income countries the rate is not known at all.

National figures often differ sharply from the global estimate. The rate recorded in any country depends on its diagnostic methods and available resources.³ So one country's rate is not a fact about autistic people everywhere; it is partly a fact about that country's services.

Recognition and diagnosis

Characteristics may be noticed in early childhood. Even so, autism is often not diagnosed until much later.¹ Signs can be harder to see in autistic women, partly because of masking. Other conditions such as anxiety or an eating disorder can obscure them further.⁵

What follows comes from the NICE guideline for autistic adults in the UK.

A clinician may use a tool such as the ADI-R, ADOS-G or DISCO. The assessment also weighs other conditions that may occur alongside autism, or that account better for what is happening. Among them are anxiety, depression, obsessive-compulsive disorder and epilepsy.⁶

NICE advises against routine biological, genetic or brain-imaging tests when assessing adults for autism.⁶ Routes into assessment differ from country to country. Check what applies where you live.

Conditions that often occur alongside autism

Autistic people often live with other conditions. WHO names epilepsy, depression, anxiety and attention deficit hyperactivity disorder,¹ and the NHS adds eating disorders to that list.² A clinical psychiatry textbook names much the same group. It lists intellectual disability, epilepsy, anxiety and attention deficit hyperactivity disorder as conditions that frequently occur alongside autism.⁷

Percentages are attached to each of these, and they shift a good deal between studies. That instability has a specific cause. The textbook attributes it to two things working together.⁷

The first is that autism is extremely heterogeneous: in plain terms, autistic people differ very widely from each other.

Its core features range from the boundary of typical development through to profound impairment. The conditions that accompany it vary just as widely.⁷ A figure drawn from one sample of autistic people may simply not describe another.

The second is a plain problem with the research. Studies often fail to replicate at follow-up, so they cannot provide reliable information. Part of the reason is the practice of publishing results from case and control groups of fewer than twenty or thirty people.⁷

The textbook describes inadequate sample size as an acknowledged problem across the whole of neuroscience. It produces failed replications and prevents a stable body of knowledge accumulating.⁷

A single striking percentage, quoted without a sample size, is usually the least reliable number on the page.

Intellectual disability is the co-occurrence that causes the most confusion, and it is widely assumed to come with autism automatically. It does not.

Intellectual functioning among autistic people varies widely, reaching from profound impairment to superior levels.¹ Some autistic people have a learning disability and many do not.

The two do frequently occur together. The diagnostic criteria treat them as separate diagnoses that can both apply to one person. To diagnose autism and intellectual disability together, a person's social communication has to be below the level expected for their general developmental stage.⁷

The rule stops difficulties that follow from a general developmental delay being counted as autism. It also stops autism being missed in someone whose overall development explains only part of what is happening.

What support actually addresses

Support does not set out to make an autistic person less autistic. It works on specific difficulties, and on the person's surroundings. WHO points to early psychosocial support that helps autistic children communicate and interact socially.¹ For adults the NICE guideline is more specific, and the table below draws on its recommendations for autistic adults.

For autistic adults, NICE advises adjusting personal space, lighting, noise and wall colour, and using visual supports.⁶ Ordinary courtesies count as well. NICE asks clinicians to use the name and title the person prefers, and to explain clinical language plainly.

One framework clinicians use is SPACE. It covers sensory needs, predictability, acceptance, communication and empathy.³ NICE tells clinicians not to provide facilitated communication for autistic adults.⁶

If you think you or someone close to you may be autistic

Recognising yourself in a description is a reasonable starting point. It is not a diagnosis, and it does not have to become one. A qualified professional can talk it through with you, and can also explain the local route to an assessment.

Being autistic is not a problem to be fixed. Understanding it usually makes life easier to arrange, at home and at work. WHO describes good care as more than clinical treatment. It includes accessibility, inclusion and support at community level.¹

You can find a therapist through TherapyRoute when you are ready.

This article is for general information and is not a substitute for professional assessment or care. If this is affecting your life, consider reaching out to a qualified mental health professional.

References

1. [1] World Health Organization. Autism (fact sheet), 17 September 2025. who.int who.int.
2. [2] NHS. What is autism? nhs.uk, page last reviewed 6 May 2026. nhs.uk/conditions/autism/what-is-autism nhs.uk/conditions/autism/what-is-autism.
3. [3] Hodis B, Mughal S, Saadabadi A. Autism Spectrum Disorder. StatPearls. Treasure Island (FL): StatPearls Publishing; last updated 17 January 2025. ncbi.nlm.nih.gov/books/NBK525976 ncbi.nlm.nih.gov/books/NBK525976.
4. [4] 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):442-62. pubmed.ncbi.nlm.nih.gov/26134030 pubmed.ncbi.nlm.nih.gov/26134030.
5. [5] NHS. Signs of autism in adults. nhs.uk, page last reviewed 6 May 2026. nhs.uk/conditions/autism/signs/adults nhs.uk/conditions/autism/signs/adults.
6. [6] National Institute for Health and Care Excellence. Autism spectrum disorder in adults: diagnosis and management. Clinical guideline CG142, last updated 14 June 2021. nice.org.uk nice.org.uk.
7. [7] Sadock, B. J., Sadock, V. A., & Ruiz, P. (Eds.) (2017). Kaplan and Sadock’s Comprehensive Textbook of Psychiatry (10th ed.). Wolters Kluwer. Chapter 44, Autism Spectrum Disorder and Social Communication Disorder, which also reprints the DSM-5 diagnostic criteria and severity specifiers.