Autism spectrum disorder (ASD) is a developmental condition that affects how children communicate, interact with others, and experience the world around them. About 1 in 31 children in the United States have ASD, based on CDC surveillance data from 2022. It’s called a “spectrum” because it shows up differently in every child: some need relatively little day-to-day support, while others need significant help with basic activities. ASD is present from early in development, though it may not be recognized until a child starts missing social or language milestones.
How ASD Affects Social Communication
The core feature of ASD is persistent difficulty with social communication and interaction. This doesn’t simply mean a child is shy or slow to warm up. It shows up in three specific ways that range from subtle to significant.
First, children with ASD often struggle with the natural back-and-forth of social exchange. A typical toddler might hold up a toy to show you, then look at your face to see your reaction. A child with ASD may not initiate that kind of sharing, or may not respond when someone else tries to engage them. In older children, this can look like one-sided conversations or difficulty understanding that communication is a two-way process.
Second, nonverbal communication is often affected. This includes eye contact, facial expressions, gestures like pointing or waving, and body language. Some children use very few gestures; others may speak fluently but rarely match their tone of voice or facial expression to what they’re saying.
Third, children with ASD frequently have difficulty building and understanding relationships. Younger children may show little interest in peers or struggle with imaginative play. Older children may want friendships but have a hard time reading social cues, adjusting their behavior to different settings, or understanding unwritten social rules.
Repetitive Behaviors and Sensory Differences
The second defining feature of ASD involves restricted, repetitive patterns of behavior, interests, or sensory responses. A child needs to show at least two of the following four patterns to meet diagnostic criteria.
- Repetitive movements or speech: This can include hand flapping, rocking, spinning, lining up toys in precise rows, or repeating words and phrases (sometimes called echolalia).
- Rigid routines and resistance to change: Some children become extremely distressed by small changes, like a different route to school or a new brand of cereal. They may insist on greeting rituals, eat the same foods daily, or follow strict self-imposed rules.
- Intense, narrow interests: Many children with ASD develop deep fascinations with specific topics or objects. The interest itself may be age-appropriate (trains, dinosaurs), but its intensity and focus stand out.
- Unusual sensory responses: A child might cover their ears at sounds that don’t bother other children, refuse to wear certain fabrics, seem indifferent to pain, or be fascinated by lights and movement. Both over-sensitivity and under-sensitivity to sensory input are common.
Early Signs by Age
ASD can sometimes be detected before a child’s second birthday, though many children aren’t diagnosed until later. The CDC highlights several early signs parents can watch for at specific ages:
- By 9 months: Does not respond to their name. Does not show facial expressions like happiness, sadness, or surprise.
- By 12 months: Does not play simple interactive games like pat-a-cake. Uses few or no gestures, such as waving goodbye.
- By 15 months: Does not share interests with others, for example by showing you a toy they like.
- By 18 months: Does not point to show you something interesting.
- By 24 months: Does not notice when others are hurt or upset.
Missing one milestone doesn’t mean a child has ASD, but a pattern of missed milestones, especially in social communication, is worth bringing up with a pediatrician. The American Academy of Pediatrics recommends that all children be screened for autism at their 18- or 24-month well-child visit using a parent questionnaire called the M-CHAT-R/F. This short checklist helps identify children who should be evaluated further.
What Causes ASD
There is no single cause. Genetic factors are estimated to contribute 40 to 80 percent of the risk for developing ASD, making heredity the strongest known influence. Changes in over 1,000 genes have been linked to the condition, though most individual gene variants contribute only a small amount of risk. ASD tends to run in families, but what’s usually inherited is an increased susceptibility, not a certainty of diagnosis.
In a small percentage of cases (about 2 to 4 percent), rare gene mutations or chromosome abnormalities appear to directly cause the condition, often alongside other medical features. For most children, though, ASD likely results from a combination of many common genetic variants interacting with environmental risk factors like older parental age and birth complications. Vaccines do not cause ASD. This has been studied extensively and definitively ruled out.
Support Levels
ASD is diagnosed at one of three support levels, which describe how much help a child needs in daily life rather than labeling them as “mild” or “severe.”
Level 1 (“requiring support”) describes children who can communicate verbally and manage many daily tasks but have noticeable difficulty initiating social interactions. They may respond to others in unusual ways or seem less interested in socializing than their peers. Repetitive behaviors are present and may interfere with some aspects of daily life.
Level 3 (“requiring very substantial support”) describes children with significant challenges in verbal communication and daily functioning. They initiate very little social interaction, respond minimally to others, and may have extremely limited speech. Fixed routines, repetitive behaviors, and intense preoccupations make it very difficult for them to cope with change or be redirected. Between 25 and 30 percent of people with ASD are nonverbal or minimally verbal, and many of them fall into this higher support category.
Level 2 falls between these two, with children needing more help than Level 1 but functioning with less restriction than Level 3. Support levels can shift over time as a child develops new skills or faces new demands.
Conditions That Often Occur Alongside ASD
Children with ASD frequently have other physical and mental health conditions. These aren’t part of ASD itself, but they’re so common that recognizing them early can make a real difference in a child’s quality of life.
Sleep problems are among the most widespread, affecting 50 to 80 percent of children with autism. Difficulty falling asleep, frequent waking, and irregular sleep patterns can worsen behavior and attention during the day. Gastrointestinal issues, including chronic constipation, diarrhea, and abdominal pain, affect up to 85 percent in some studies. Many children also have significant feeding challenges and food selectivity.
ADHD is one of the most commonly co-occurring psychiatric conditions. In fact, as many as 85 percent of children with autism have at least one additional psychiatric diagnosis, with ADHD, anxiety, and depression being the most frequent. Epilepsy is also strikingly common, affecting 25 to 40 percent of children with ASD compared to 2 to 3 percent of the general population. Obesity rates are roughly double the general childhood population, at about 30 percent.
Therapies and Support
There is no single treatment for ASD, but several evidence-based therapies can help children build skills and participate more fully in daily life. Most children benefit from a combination of approaches, and starting early tends to produce better outcomes.
Speech and language therapy is the most common developmental therapy for children with ASD. It helps children improve their understanding and use of language, whether that means building first words, learning to hold a conversation, or developing alternative communication methods for children who are nonverbal.
Applied behavior analysis (ABA) is the most widely studied behavioral approach. It works by reinforcing desired behaviors and teaching new skills in structured, measurable steps. ABA programs vary widely in intensity and style, from clinic-based sessions several hours a week to naturalistic play-based models.
Occupational therapy focuses on the practical skills needed for independence: dressing, eating, bathing, handwriting, and managing sensory sensitivities. For children who are overwhelmed by certain textures, sounds, or environments, occupational therapists can use sensory integration techniques to help them gradually tolerate and respond more comfortably to sensory input.
The right combination of therapies depends on a child’s age, support level, and specific strengths and challenges. What helps one child may not be the best fit for another, which is why individualized planning matters more than following a single protocol.