What is ASD?

ASD is defined by two core areas of difference that must both be present: persistent difficulties in social communication and social interaction, and restricted or repetitive patterns of behavior, interests, or activities. These differences must be present from early in development, even if they are not recognized until later in life—often because a person has developed strategies to mask or compensate for them.

ASD is not a degenerative condition. It does not get worse over time in the way that some illnesses do. People with ASD may make substantial gains with support and experience, though the underlying differences in how they think and perceive the world remain part of who they are. Levels of independence and daily functioning vary widely across the spectrum.

ASD is distinct from intellectual developmental disorder, though the two can co-occur. Many autistic people have average or above-average intelligence.

Social communication and interaction

All three of the following must be present (currently or by history):

Social-emotional reciprocity—difficulty with the back-and-forth of social interaction; this may look like reduced sharing of interests or emotions, not responding typically in conversation, or not initiating social exchange in expected ways
Nonverbal communication—difficulty integrating verbal and nonverbal communication; may include reduced eye contact, limited use of gesture, atypical facial expression, or difficulty reading others' nonverbal cues
Developing and maintaining relationships—difficulty adjusting behavior to different social contexts, making friends, or understanding the unwritten rules of social interaction

Restricted and repetitive behaviors

At least two of the following must be present:

Repetitive movements, use of objects, or speech—such as hand-flapping, rocking, lining up objects, or echolalia (repeating words or phrases)
Insistence on sameness—strong adherence to routines, distress at small changes, rigid thinking patterns, or needing to do things in a specific order
Highly focused interests—intense, narrow interests that are unusual in their focus or depth; these can also be a significant source of joy, skill, and connection
Sensory differences—being particularly sensitive or under-sensitive to sounds, textures, light, temperature, pain, or other sensory input; this can have a major impact on daily life and comfort

Support levels

ASD is described across three levels of support need, reflecting the impact of the condition on daily functioning:

Level 1 — Requiring support

Without support in place, noticeable difficulties with social communication exist. The person may be able to speak in full sentences and engage in social situations, but the back-and-forth of conversation is difficult and attempts to make friends may be unsuccessful. Inflexibility causes some interference in one or more areas of life.

Level 2 — Requiring substantial support

Marked difficulties in social communication are apparent even with support in place. The person may initiate interactions in limited ways and respond mainly to direct approaches. Repetitive behaviors and resistance to change are noticeable and cause difficulties across settings.

Level 3 — Requiring very substantial support

Severe difficulties in social communication significantly limit functioning. Very limited verbal and nonverbal social communication. Extreme difficulty coping with change, with restricted/repetitive behaviors that markedly interfere with functioning across all areas.

How common is it?

1–2%

estimated prevalence in the U.S.

3:1

ratio of males to females diagnosed

Later

diagnosis is common in girls and women, who are more likely to mask

ASD is more commonly diagnosed in males, but girls and women are significantly underdiagnosed. Girls often learn to mask or camouflage their autistic traits—mirroring social behavior they observe in others—which can make the diagnosis less apparent and delay identification by years or decades. This masking takes a toll on mental health.

Underdiagnosis is also common in people from marginalized groups, where cultural differences in social norms can influence how autistic traits are perceived and whether families seek or receive assessment.

When do symptoms appear and how does ASD progress?

Differences are present from early in development, though they may not be recognized or become clearly impairing until later—sometimes not until social demands exceed a person's ability to compensate, which can be in secondary school, university, or adulthood. ASD is a lifelong condition, but it is not degenerative. Many autistic people develop skills, strategies, and a better understanding of themselves over time.

Functional outcomes vary enormously. Some autistic people live fully independently, hold demanding careers, and have rich social lives. Others require significant daily support. The level of support needed is not a measure of a person's value or potential.

Risk factors

Genetics

ASD is highly heritable. Many genes contribute to risk—there is no single "autism gene." Having a sibling or parent with ASD significantly raises a person's own likelihood. In some cases, ASD is associated with a known genetic condition such as Fragile X syndrome.

Prenatal and birth factors

Advanced parental age at conception, premature birth, and prenatal exposure to certain medications—such as valproic acid—are associated with increased risk. These are risk factors, not causes, and most children exposed to these factors do not develop ASD.

ASD and suicidal thoughts

Autistic people are at elevated risk of suicidal ideation and attempts, particularly those with co-occurring psychiatric conditions such as depression or anxiety. The daily experience of navigating a world not designed for neurodivergent people—including masking, social rejection, and misunderstanding—contributes significantly to this risk. If you or someone you know is struggling, please reach out for help.

988 Suicide & Crisis Lifeline: Call or text 988 (available 24/7 in the U.S.)

Conditions that often occur alongside ASD

ASD rarely occurs in isolation. Common co-occurring conditions include:

ADHD
Anxiety disorders
Depressive disorders
Obsessive-compulsive disorder (OCD)
Intellectual developmental disorder
Language disorder
Sleep disorders
Epilepsy

Identifying and supporting co-occurring conditions is an important part of overall care. Anxiety and depression in particular are common and treatable, and addressing them can significantly improve quality of life.

What to do next

If you are concerned that you or your child may be autistic, speaking with a GP is a good starting point. A formal diagnostic assessment—conducted by a psychologist, psychiatrist, or specialist team—will look at development history, current functioning, and behavior across different settings.

A diagnosis can open the door to appropriate support, accommodations at school or work, and a clearer understanding of oneself. Many autistic people find that a diagnosis—even in adulthood—brings significant relief and a framework for understanding their experiences.

Support following a diagnosis may include speech and language therapy, occupational therapy, psychological support for co-occurring conditions such as anxiety, and practical accommodations. The most effective support is tailored to the individual's specific profile of strengths and needs.