Autism spectrum disorder (ASD) is a developmental condition that affects how a person communicates, interacts socially, and experiences the world around them. About 1 in 31 children in the United States (3.2%) have been identified with ASD, making it one of the most common neurodevelopmental conditions. The word “spectrum” reflects the wide range of ways autism presents: some people need significant daily support, while others live independently with few outward signs.
Core Traits of Autism
A diagnosis of ASD rests on two categories of traits. The first involves differences in social communication and interaction. This can look like difficulty with back-and-forth conversation, reduced sharing of emotions or interests, limited use of gestures and facial expressions, or trouble building and maintaining relationships. These differences show up across multiple settings, not just one.
The second category involves restricted or repetitive patterns of behavior. A person needs to show at least two of four types: repetitive movements, speech, or use of objects (like lining things up or echoing phrases); a strong need for sameness and routines, with distress when they’re disrupted; intensely focused interests that go beyond what’s typical in depth or subject matter; and unusual sensitivity to sensory input, whether that’s being overwhelmed by certain sounds or textures, or seeming barely to notice pain or temperature changes.
These traits must be present from early in development, though they don’t always become obvious right away. In some people, they only surface when social expectations increase beyond what they can manage, or they may be hidden by strategies the person has learned over time.
Early Signs in Toddlers
Some of the earliest indicators involve how a child shares attention with a caregiver. By 12 months, most children will follow a parent’s pointed finger to look at something, then look back at the parent and mirror their expression. A child on the autism spectrum may not track the point or check back with the parent. By 15 months, most children point at things they want. An autistic child may instead take a parent’s hand and physically guide it to the object, often without making eye contact.
By 18 months, a key difference emerges in why a child points. Most toddlers point to share their excitement about something interesting, looking back and forth between the object and the parent. A child with autism is more likely to point only as a way to request something, not to share the experience. About 25% of children later diagnosed with autism develop some language and then gradually or suddenly stop using it, typically between 15 and 24 months. This loss of skills, called regression, can also include becoming more socially withdrawn.
What Causes Autism
Autism is strongly genetic. Heritability estimates based on family studies sit at roughly 80%, with hundreds of genes collectively increasing the likelihood. No single gene causes autism on its own. Instead, many genetic variations each contribute a small amount of risk.
Environmental factors account for about 40% of the variance seen in twin studies, meaning genetics and environment overlap and interact rather than adding up neatly to 100%. Factors linked to higher likelihood include advanced parental age, short gaps between pregnancies, and certain maternal health conditions during pregnancy such as autoimmune disease, high blood pressure, obesity, diabetes, or infection. Prenatal exposure to air pollution, pesticides, and the seizure medication valproate have also been associated with increased risk. On the protective side, prenatal folic acid supplementation is linked to lower autism likelihood and may buffer against some environmental exposures.
Perinatal factors like premature birth, complications during delivery, and oxygen deprivation at birth are also associated with autism, and these may partly explain the connection to maternal health conditions.
What’s Different in the Brain
Research from Yale School of Medicine found that autistic adults had 17% lower synaptic density across the whole brain compared to non-autistic adults. Synapses are the connections neurons use to pass information to each other, so fewer synapses means the brain’s communication network is wired differently. The study also found a direct correlation: the lower someone’s synaptic density, the more pronounced their social communication differences were, including reduced eye contact, repetitive behaviors, and difficulty reading social cues. This was a small study (12 autistic and 20 non-autistic adults), but it was the first to measure this difference in living people rather than in postmortem tissue.
Gender and Diagnosis
Autism has historically been considered far more common in males, with ratios around 3 to 1 in childhood diagnoses. But that gap is closing fast. A large population-based study published in The BMJ found that by 2022, the cumulative male-to-female ratio for autism diagnosis had dropped to 1.2 by age 20. The researchers projected this ratio would reach parity by 2024.
The shrinking gap reflects improved recognition of autism in girls and women rather than a true change in who is autistic. Several factors have historically kept females from being diagnosed. Girls tend to have stronger baseline social and communication skills, which can make their autistic traits harder to spot using assessment tools originally designed around how autism presents in boys. Females are also more likely to camouflage their differences by mimicking peers’ speech, expressions, and social behavior. And co-occurring conditions like anxiety or depression sometimes overshadow the underlying autism, leading clinicians to diagnose only the more visible condition.
Masking and Autism in Adults
Many autistic people, particularly those diagnosed later in life, develop a strategy called masking. This involves observing, analyzing, and mirroring the behaviors of people around them while tightly controlling their own self-expression. In practice, it looks like forcing or carefully monitoring eye contact, using rehearsed facial expressions, changing speech patterns or tone of voice, suppressing the urge to stim (self-soothing repetitive movements), and scripting conversations in advance.
Masking can be conscious or unconscious. Either way, it means manually performing social behaviors that come naturally to non-autistic people, and it is exhausting. Over time, this constant self-monitoring can lead to what’s called autistic burnout: a period of intense fatigue, reduced ability to function, and increased sensitivity. Masking also contributes to mental health difficulties, partly because the person may lose touch with their own needs and identity in the process of constantly adapting to others’ expectations.
Conditions That Often Co-Occur
Autism rarely exists in isolation. Up to 84% of autistic individuals experience some form of anxiety, including social anxiety, generalized anxiety, phobias, and obsessive-compulsive patterns. Epilepsy affects up to 35% of autistic people, compared to about 1% of the general population. Autistic children are roughly four times more likely to have gastrointestinal problems than their non-autistic peers. These aren’t part of autism itself, but they’re common enough that they shape daily life for many autistic people and often need their own support.
Therapies and Support
There is no single treatment for autism because it isn’t a single set of challenges. Support is tailored to the individual. The most widely used approach is applied behavior analysis (ABA), which works by reinforcing helpful skills and reducing behaviors that get in the way of daily life. ABA has strong evidence behind it, though it varies significantly in quality and philosophy depending on the provider. Some autistic adults have criticized older, more rigid versions of ABA for prioritizing outward compliance over the person’s comfort and autonomy, and modern programs increasingly focus on building skills the person actually wants and needs.
Speech and language therapy helps with understanding and using spoken language, which can range from building first words to improving conversational flow in someone who already speaks fluently. Occupational therapy focuses on practical independence: dressing, eating, bathing, navigating sensory environments, and relating to other people. Sensory integration therapy, often delivered within occupational therapy, helps people manage responses to sensory input that might otherwise feel overwhelming or disorienting.
The right combination depends on the person’s age, what they find challenging, and what goals matter most to them or their family. Many autistic people benefit most not from changing their behavior but from adjusting their environment, finding accommodations at school or work, and building a life that works with how their brain operates rather than against it.