Autism, or autism spectrum disorder (ASD), is a developmental condition that affects how a person communicates, interacts with others, and experiences the world around them. About 1 in 31 children in the United States has been identified with autism, based on CDC surveillance data from 2022. It’s called a “spectrum” because it looks different from person to person, ranging from those who need minimal day-to-day support to those who need help with basic activities.
The Two Core Features of Autism
Autism involves two broad areas of difference. The first is social communication. Autistic people may have difficulty with back-and-forth conversation, reading facial expressions or body language, or understanding the unspoken social rules that others seem to pick up naturally. Some people speak fluently but struggle to maintain friendships; others may not use spoken language at all.
The second area involves repetitive behaviors and restricted interests. This can show up in many ways: repeating certain movements (like hand-flapping or rocking), needing to follow the same routine every day, developing intensely focused interests in specific topics, or reacting strongly to sensory input like loud sounds, bright lights, or certain textures. A child might line up toys in a precise order and become very upset if someone rearranges them. An adult might eat the same meal every day and find comfort in that consistency.
For a diagnosis, a person needs to show persistent differences in all three aspects of social communication (reciprocity, nonverbal cues, and relationships) plus at least two of the four types of repetitive or restricted behaviors. These patterns need to be present from early in development, though they don’t always become obvious until later in life when social demands increase.
What Happens in the Brain
Autism has a strong biological basis. Research at Columbia University found that children and adolescents with autism have a surplus of synapses, the tiny connections between brain cells. During typical development, the brain produces a burst of these connections in infancy and then “prunes” about half of them by late adolescence. In autistic children’s brains, that pruning process slows dramatically, reducing connections by only about 16% compared to the typical 50%. The result is a brain with significantly more neural connections, which changes how information is processed.
Researchers traced this pruning difference to an overactive protein that interferes with the brain’s ability to clear out old and damaged cellular material. This isn’t something caused by parenting or lifestyle. It’s a fundamental difference in how the brain develops and organizes itself.
Causes and Risk Factors
Genetics play the largest role. Heritability estimates sit at roughly 80% based on family studies, with hundreds of genes contributing small increases in likelihood rather than a single “autism gene.” Having an autistic sibling substantially raises the odds of a child being autistic as well.
Environmental factors account for about 40% of the variance seen in twin studies. These include advanced parental age, short gaps between pregnancies, and maternal health conditions like autoimmune disease, high blood pressure, obesity, or diabetes during pregnancy. Fetal exposure to air pollutants, pesticides, and certain medications has also been linked to increased likelihood. On the protective side, prenatal folic acid supplementation is associated with decreased autism likelihood. Complications during birth, including prematurity and oxygen deprivation, are additional risk factors.
Early Signs in Children
Some signs can appear before a child’s first birthday. A baby who doesn’t respond to their name by 9 months, or who doesn’t show a range of facial expressions like happy, sad, or surprised by the same age, may warrant closer attention. By 12 months, most children play simple interactive games like pat-a-cake and use gestures like waving goodbye. The absence of these milestones is one of the earliest flags.
Between ages 1 and 2, the signs often become clearer. A child who doesn’t point to share something interesting by 18 months, or who doesn’t seem to notice when others are hurt or upset by age 2, may be showing early characteristics of autism. By age 3, most children naturally seek out other kids and join in play. By 4, they engage in pretend play, acting like a teacher or superhero. Delays or absence of these behaviors doesn’t guarantee autism, but they’re worth discussing with a pediatrician.
How Autism Looks Different in Girls
Autism has historically been diagnosed far more often in boys, but a growing body of research suggests many girls and women are missed. One major reason is camouflaging: the practice of consciously or unconsciously hiding autistic traits to fit in socially. Common camouflaging strategies include forcing eye contact, suppressing repetitive hand movements, using memorized conversational scripts, and relying on learned rules to interpret other people’s body language.
Girls with autism often develop these strategies early by carefully observing and imitating their peers. This can make them appear socially competent on the surface while they’re working extremely hard underneath. Research shows that autistic people of all genders use camouflaging to navigate a world built around non-autistic social norms, often at significant personal cost, including exhaustion, anxiety, and burnout. The fact that girls tend to camouflage more heavily helps explain why they’re frequently diagnosed later or not at all.
The Three Support Levels
Rather than labeling autism as “mild” or “severe,” clinicians assign one of three support levels, and they do so separately for each of the two core areas. This means a person might need minimal support with communication but substantial support with repetitive behaviors, or vice versa.
Level 1 (“requiring support”) describes someone who can communicate but may need prompting to ask for help or coaching to understand nonverbal cues like facial expressions. Level 2 (“requiring substantial support”) might describe a person whose intense focus on specific interests causes significant distress when they need to shift attention to something else, like schoolwork. Level 3 (“requiring very substantial support”) includes people who may not yet use words or gestures to communicate their needs and who require hands-on help throughout the day. These levels aren’t permanent. A person’s support needs can change over time with development and the right interventions.
Conditions That Often Come With Autism
Autism rarely shows up alone. ADHD, anxiety, and depression are the most commonly diagnosed co-occurring conditions. Chronic sleep problems affect between 50% and 80% of autistic children, making daily functioning harder for the whole family. Gastrointestinal issues, including chronic constipation, diarrhea, and abdominal pain, affect up to 85% of autistic individuals in some studies, though estimates vary widely.
These overlapping conditions can sometimes mask autism itself. A child might be treated for anxiety or ADHD for years before someone recognizes that autism is the underlying factor shaping their experience.
How Autism Is Diagnosed
There’s no blood test or brain scan for autism. Diagnosis relies on behavioral observation and developmental history. The gold-standard tool is the Autism Diagnostic Observation Schedule (ADOS-2), a structured observation session where a trained clinician creates social situations and evaluates how the person responds. It requires extensive, specialized training to administer and interpret correctly, which is why evaluations are best done by specialists rather than general practitioners. The ADOS-2 is typically paired with a detailed parent or caregiver interview that covers the person’s developmental history from infancy onward.
Wait times for a formal evaluation can be long, sometimes months to over a year depending on location. Pediatricians can do initial screening as early as 18 months, which helps identify children who should be referred for a full evaluation.
Therapies and Support
There is no single treatment for autism, but a range of therapies can build skills and improve quality of life. Speech and language therapy helps with understanding and using communication, whether that means spoken words, sign language, or communication devices. Occupational therapy focuses on daily living skills like dressing, eating, and managing sensory sensitivities. Sensory integration therapy specifically targets responses to input that feels overwhelming or goes unnoticed.
Applied behavior analysis (ABA) is one of the most widely used behavioral approaches. It works by reinforcing desired behaviors and teaching new skills through structured, step-by-step practice. Some programs focus on building “pivotal skills,” like initiating communication, that unlock progress in many other areas at once. The Early Start Denver Model blends play and social interaction in natural settings to build language and social skills in very young children.
Social skills groups give autistic people a structured space to practice interactions like starting conversations, taking turns, and reading social cues. For children in school, educational approaches can adapt classroom environments to support learning, using visual schedules, structured routines, and clear organization to reduce overwhelm. Relationship-based approaches encourage parents and therapists to follow the child’s interests, using what naturally motivates them as a bridge to communication and connection.
The most effective support plans are tailored to the individual. What helps one autistic person may be irrelevant or even counterproductive for another, which is exactly why it’s called a spectrum.