What is autism?

Autism is not an illness someone catches, and it is not a personality type. It is a different way a brain develops, present from early childhood and lasting across life. How visible it is varies hugely: one autistic adult may need help with daily living, while another runs a team at work and only realizes in their forties why open-plan offices leave them wrecked by Wednesday.

What is autism spectrum disorder?

"Autism spectrum disorder", often shortened to ASD, is the formal diagnostic name used in the DSM-5-TR (the US psychiatric manual) and in ICD-11 (the World Health Organization classification used in most of the world). Since 2013 it has covered what used to be several separate labels, including Asperger syndrome and pervasive developmental disorder not otherwise specified. Many autistic adults simply say "autism" or "autistic", and some still identify with the older term Asperger's.

In broad terms, a diagnosis rests on two groups of features, both present since early development and both making a real difference to daily life:

• Differences in social communication and interaction: for example, finding unwritten social rules hard to read, using or reading facial expressions and tone differently, or finding back-and-forth small talk draining.
• Restricted or repetitive patterns of behavior, interests or activities: for example, strong reliance on routine, deep focused interests, repetitive movements (stimming), or sensory sensitivity such as being overwhelmed by noise, light, smells or textures.

This is a plain summary, not the official criteria. A clinician uses the full criteria, a developmental history and often information from someone who knew you as a child.

What does "spectrum" actually mean?

People often picture the spectrum as a line from "a little autistic" to "very autistic". That picture misleads. The spectrum is closer to a set of separate dials: sensory sensitivity, social communication, need for predictability, focus, motor coordination, language. Each autistic person has a different setting on each dial, and the settings can shift with stress, sleep, environment and age.

So two autistic adults can look very different. One speaks fluently, works as an engineer and struggles mostly with sensory overload and exhaustion after social events. Another uses a communication device and needs daily support. Both are autistic. The DSM-5-TR adds support levels (1 to 3) to describe how much support someone needs in each area, but these describe needs at a point in time, not a fixed rank of the person.

• Autism levels 1, 2 and 3 explainedAutism levels 1, 2 and 3 explained: what DSM-5 support levels describe, how clinicians assign them, why they are criticized, and why no quiz gives one.
• DSM-5 autism criteria in plain languageThe DSM-5-TR autism criteria in plain language for adults: the two core areas, early onset and masking, impairment, ICD-11 6A02, with adult examples.

What is autism considered or classified as?

Clinical category

Neurodevelopmental condition (DSM-5-TR and ICD-11)

ICD-11 code

6A02 Autism spectrum disorder

Is it an illness?

No. Health bodies describe it as lifelong and present from birth, not an illness.

Is it a learning disability?

No, though a minority of autistic people also have one

Legal status

Often recognized as a disability under laws such as the ADA (US) and Equality Act 2010 (UK)

Our separate page on whether autism is a mental disorder goes into this more deeply, including the neurodiversity view of autism as a natural variation and the reasons many people still find the medical framing useful for getting support.

How autism often shows up in adults

Adult autism tends to look less like the childhood stereotype and more like a pattern of costs and preferences. Things adults commonly describe include:

• Needing long recovery time after social events, even ones they enjoyed.
• Rehearsing conversations or phone calls beforehand and replaying them afterward.
• Strong reactions to sensory input: fluorescent lights, background chatter, clothing tags, certain food textures.
• A preference for clear, direct communication and frustration with hints or vague instructions.
• Deep, absorbing interests that can fill hours without noticing time pass.
• Distress when plans change at short notice, even small changes.

• Autistic masking: what it is and what it costsAutistic masking means hiding or compensating for autistic traits to fit in. See real adult examples, why people mask, what it costs, and how to mask less.
• Autism in women: the signs that often go unnoticedAutism in women often looks different from the stereotype. Learn the signs autistic women commonly describe, the role of masking, and why many are missed.

What autism is not

• Not caused by parenting style, vaccines or anything a person did. Research points mainly to genetics.
• Not a lack of feeling. Many autistic people feel strongly; differences are often in how emotions are read or expressed.
• Not something people grow out of, though skills, coping strategies and support needs can change over life.
• Not tied to any level of intelligence. Autistic people span the full range of intellectual ability.

Autism also often comes with company. ADHD, anxiety, depression, epilepsy and sleep problems are more common among autistic people than in the general population, and these can shape daily life as much as autism itself. A good assessment looks at the whole picture.

A note on language

This site mostly says "autistic adults" because surveys of the UK autism community found that many autistic adults prefer identity-first language. Some people prefer "person with autism", and that choice is equally valid. Use the words the person in front of you uses.

What to do if this sounds familiar

• How to get tested for autism as an adultYes, adults can be tested for autism. The practical steps: preparing notes, getting a referral, choosing an assessor, paying, and what the result means.
• Autism research, prevalence and mythsWhat research says about autism: how common it is, sex differences, genetics, intelligence, double empathy, classification and the myths that persist.