Autism has traditionally been described by three core characteristics: differences in social interaction, differences in communication, and restricted or repetitive patterns of behavior. This framework, known as the “triad of impairments,” was established by researchers Lorna Wing and Judith Gould in 1979 and shaped how autism was understood for decades. The current diagnostic manual (DSM-5) has since merged social interaction and communication into a single category, creating two broad domains instead of three. But the three original characteristics remain widely referenced and still capture what autism looks like in everyday life.
Where the “Three Characteristics” Come From
Wing and Gould studied the prevalence of autism in children and identified a group (about 15 per 10,000 at the time) who shared difficulties in three areas: social interaction, communication, and imagination. They also noted a pattern of narrow, repetitive activities. This triad became the standard framework for decades, influencing diagnostic criteria worldwide.
When the DSM-5 was published in 2013, it folded social interaction and communication together into one domain, reasoning that the two are deeply intertwined. The result is two diagnostic pillars: persistent deficits in social communication and interaction, plus restricted and repetitive behaviors. If you’ve seen sources citing “two” characteristics and others citing “three,” that’s why. The underlying traits haven’t changed, just how they’re grouped. Current CDC data estimates about 1 in 31 children are identified with autism, based on 2022 surveillance across 16 U.S. sites.
Social Interaction Differences
The first of the original three characteristics involves how a person connects with others socially. This includes what clinicians call social-emotional reciprocity, the natural back-and-forth rhythm of interaction. In practice, this might look like difficulty with conversational turn-taking, reduced sharing of emotions or interests, or not initiating social contact in typical ways. An autistic person might not instinctively respond when someone shares exciting news, or may struggle to gauge when it’s their turn to speak.
Relationship development also falls under this umbrella. Some autistic people find it hard to adjust their behavior across different social settings, like shifting from a casual tone with friends to a more formal one at work. Others may have little interest in peer relationships, or may want friendships but find the unwritten rules of maintaining them confusing. In young children, this can show up as not joining other children in play by age 3, or not engaging in pretend play (like pretending to be a superhero) by age 4.
These differences show up early. A child who doesn’t respond to their name by 9 months, doesn’t play simple interactive games like pat-a-cake by 12 months, or doesn’t share interests with others by 15 months may be showing early signs. Not noticing when others are hurt or upset by age 2 is another marker the CDC highlights.
Communication Differences
The second characteristic involves how a person uses and understands both verbal and nonverbal communication. This goes well beyond speech. Many autistic people have difficulty reading body language, understanding gestures, or interpreting facial expressions. Some use limited eye contact or have facial expressions that don’t match the social context. Others may speak fluently but struggle with the pragmatic side of language: sarcasm, implied meaning, or knowing how much detail to include in a conversation.
In children, early signs include using few or no gestures (like waving goodbye) by 12 months, not pointing to show you something interesting by 18 months, or repeating words and phrases (a pattern called echolalia). Some autistic children develop speech on a typical timeline but use it in unusual ways, like reciting scripts from shows instead of generating spontaneous sentences. Others are nonspeaking or minimally speaking and may communicate through alternative methods.
The DSM-5 merged this with social interaction because the two are so closely linked. Difficulty reading someone’s facial expression, for instance, is both a communication challenge and a barrier to social connection. In daily life, the distinction often doesn’t matter. What matters is that the person experiences the social world differently.
Restricted and Repetitive Behaviors
The third characteristic covers a wide range of patterns that fall into four subtypes. A person needs to show at least two of these four to meet diagnostic criteria.
- Repetitive movements, speech, or use of objects. This includes hand flapping, rocking, spinning, lining up toys in precise order, or repeating specific phrases. In children, getting upset when the order of lined-up objects is changed is a common example.
- Insistence on sameness and rigid routines. This might look like extreme distress over small changes, needing to take the same route every day, eating the same foods, or following greeting rituals. Transitions between activities can be particularly difficult.
- Intense, focused interests. Many autistic people develop deep expertise in specific topics. The interest itself may not be unusual (trains, weather patterns, a particular video game), but the intensity and focus are. A child might fixate on a single part of a toy, like the wheels on a car, rather than playing with it in the expected way.
- Sensory differences. This was added as a formal criterion in the DSM-5 and includes both over-sensitivity and under-sensitivity to sensory input. Some autistic people have strong negative reactions to specific sounds or textures. Others seem indifferent to pain or temperature. Excessive smelling or touching of objects, or a fascination with lights and movement, also falls here.
These behaviors serve real purposes. Repetitive movements can be calming or help with self-regulation. Routines provide predictability in a world that can feel overwhelming. Intense interests are often a source of genuine joy and competence.
How These Traits Look Different Across People
Autism is a spectrum, and these three characteristics show up with enormous variation. The DSM-5 defines three support levels. Level 1 (“requiring support”) describes someone who can function independently in many areas but struggles noticeably in social situations without support. Level 3 (“requiring very substantial support”) describes someone with severe difficulties in communication and daily functioning. Most autistic people fall somewhere along this range, and their support needs can shift over time or across different environments.
Gender plays a role in how autism presents. Women and girls are more likely to camouflage their traits, consciously or unconsciously adjusting their behavior to blend in. Techniques include forcing eye contact, imitating others’ social movements, scripting conversations in advance, and suppressing natural tendencies like stimming. This masking makes autism harder to identify in women, contributing to later diagnosis and years of struggling without understanding why social life feels so exhausting.
Age matters too. A toddler who doesn’t respond to their name and lines up toys looks very different from an adult who holds a steady job but feels drained after every social interaction. The core characteristics are the same, but their expression changes with development, learned coping strategies, and the demands of different life stages.
Sensory Differences as a Defining Feature
Sensory processing deserves extra attention because it was only formally recognized as a diagnostic criterion in 2013, despite being reported by autistic people for decades. For many, sensory experiences are among the most impactful aspects of daily life. A fluorescent light that a non-autistic person barely notices might be painfully distracting. The texture of certain clothing can feel intolerable. Conversely, some autistic people seek out specific sensory input, like deep pressure or repetitive visual patterns, because it feels regulating.
Sensory differences can also explain behaviors that might otherwise seem puzzling. A child covering their ears in a noisy cafeteria isn’t being difficult; they’re overwhelmed. An adult who avoids restaurants may not be antisocial but unable to filter out the competing sounds, smells, and visual chaos. Understanding sensory processing as a core feature of autism, rather than a quirk, changes how these behaviors are interpreted and supported.