Autism spectrum disorder affects how a person communicates, behaves, and experiences the world. Since autism is a spectrum of neurological and developmental disorders, symptoms can vary widely between individuals. Some people may only show subtle differences, while others might need substantial support. These behaviors can also vary with age — the characteristics of autism look different in infants, toddlers, older children, adolescents, and adults.

Understanding these patterns can help family members recognize early signs of autism to better support their loved one. Many treatments have proved effective at improving outcomes for people with autism. Read more about autism treatments.

What Is the Biggest Indicator of Autism?

There isn’t a single sign or indicator that someone has autism. Instead, healthcare providers look at patterns of behavior to create a bigger picture. The Diagnostic and Statistical Manual of Mental Disorders (DSM-5-TR) lays out symptom criteria for the diagnosis of autism spectrum disorder in two areas:

• Social communication and social interaction
• Restricted, repetitive patterns of behavior, interests, or activities

These two areas focus on how autism can show up in daily life. Continue reading to learn more about the most common autism symptoms.

1. Social and Communication Differences

Differences in social and communication skills are often among the earliest signs of autism. These behaviors can look different as a person ages.

Babies and Toddlers

Early symptoms of autism in babies may include:

• Not making eye contact
• Not responding to their name by 12 months
• Not looking at what their parent points to
• Not pointing at objects to show their interest by 15 months
• Not pointing at interesting things for the parents to notice by 18 months
• Not saying “mama” or “dada” by about 12 months
• Not using simple gestures by about 12 months

Although children as young as 12 months can be screened for autism, it may not be possible to get a reliable diagnosis until they are a little older.

Children

As children grow, some may show developmental delays — in which social and language skills develop more slowly. Other children may lose social and language skills they once had. Children with autism may:

• Remain nonverbal, have limited speech, or lose speech milestones
• Repeat words or phrases (also called echolalia)
• Have difficulty using or interpreting body language, such as pointing or shaking the head
• Prefer to be alone
• Dislike cuddling and avoid physical contact
• Be reluctant or unable to engage with others
• Show no interest in games that involve pretending, or only pretend if it is a favorite topic
• Lack awareness of others
• Not understand their own emotions or the emotions of others
• Prefer familiar routines

Adolescents and Adults

By adolescence and adulthood, many autistic people have developed coping behaviors to adapt to social and communication challenges. Still, other behaviors may remain noticeable, including:

• Deep knowledge and interest in one narrow topic and difficulty discussing other topics
• Tendency to go into long monologues on their favorite topic
• Difficulty understanding how others feel or think
• Trouble interpreting social cues or hints and nonverbal communication, such as body language and facial expressions
• Difficulty keeping up a conversation
• Standing closer than their peers during conversations
• Strict adherence to routines
• Difficulty around transitions and changes

2. Repetitive and Restricted Behaviors

Patterns of repetitive behaviors and restricted interests and activities are a hallmark of autism. Many repetitive behaviors are a form of self-stimulatory behavior, also known as stimming. For people with autism, stimming can provide calm or comfort in a stressful or overstimulating environment or help focus attention.

Repetitive Patterns or Behaviors

Repetitive patterns can take many forms, including:

• Hand flapping
• Rocking or spinning
• Head bobbing
• Arranging and rearranging toys or objects
• Rigidly insisting on a routine
• Making repetitive noises
• Pacing

Many people — both autistic and nonautistic — might engage in stimming behaviors. However, for autistic people, these behaviors are important to their emotional well-being. When autistic people hide or suppress stimming behaviors, it can cause anxiety and distress.

Focused Interests and Activities

An intensely focused interest can be a core sign of autism. Many autistic people have a focused and dedicated interest that brings them joy. Unlike a hobby that might be enjoyable during leisure time, these interests often become a crucial part of an autistic person’s well-being.

An autistic person may spend a lot of time learning about, thinking about, or engaging in a particular interest. They might collect items, media, or materials related to their interest. For many autistic people, their focused interest helps them manage stress, regulate their emotions, and relax.

Preference for Routine

Many autistic people have a strong preference for order and a predictable routine. This might look like:

• Eating the same meal every day
• Completing tasks in the same order
• Using a favorite item in a socially odd way or at a later developmental stage than peers
• Keeping items or toys lined up or well organized
• Needing to know the exact order of events

Sticking to routines and rituals can help autistic people cope with stress.

What Are the Behavioral Problems of Autism?

Repetitive and restrictive behaviors themselves aren’t behavioral problems. They’re often coping behaviors of autism to help regulate emotions and stress. If the behaviors are not socially acceptable, an autistic person may be distressed by not being allowed to engage in them. Autistic people do need additional support if these behaviors are harmful or dangerous, such as:

• Self-injurious behaviors, such as biting or head banging
• Repetitive behaviors that can cause significant emotional distress (such as in obsessive-compulsive disorder)
• Rigid adherence to routines so that any changes cause significant distress

3. Sensory Processing Differences

Sensory processing refers to how your brain interprets information from the world around you. People with sensory processing differences may have trouble receiving and interpreting sensory information. That includes information from your five senses, as well as your balance, body awareness, and internal signals. Research indicates that between 53 percent and 95 percent of autistic people have sensory processing differences.

Some people may be hypersensitive to sensory input, including:

• Bright lights
• Cluttered environments
• Loud sounds
• Background noise
• Strong smells
• Flavors
• Textures
• Temperatures

Other people may be less sensitive to sensory input (hyposensitive). They may not notice sights or sounds that others do. This can lead to boredom and seeking out stronger sensory experiences. Some autistic people can have a mix of both hyper- and hyposensitivity that vary by sense and environment.

4. General Symptoms

In addition to issues with communication, difficulty in social situations, and repetitive behaviors, many people with autism experience general symptoms.

Intellectual and Cognitive Differences

Approximately one-third of autistic people have intellectual disabilities, while others have average or significantly above-average intellectual abilities.

Cognitive (thinking) patterns that display rigid or literal thinking are common in people with autism. Children with autism may lack awareness of or fear of danger. Others may interpret people with autism as lacking in “common sense.”

Sleep Problems

Sleep issues are extremely common in people with autism. It’s estimated that between 50 percent and 80 percent of autistic people have sleep problems. People with autism may have trouble getting to sleep, wake up repeatedly during the night, or wake very early in the morning.

Factors like anxiety, gastrointestinal discomfort, or medication side effects can make it more difficult to sleep. Poor sleep can worsen learning difficulties, hyperactivity, and behavioral challenges.

Gastrointestinal Problems

Autistic children are about four times more likely to experience gastrointestinal (digestive) problems than nonautistic children. The most common gastrointestinal problems include:

• Constipation
• Diarrhea
• Abdominal (stomach) pain
• Food restrictions, often due to textures

There is some evidence that the makeup of intestinal bacteria may differ between people who have autism and people who don’t. Differences in intestinal bacteria could influence digestive problems. More research is needed to determine the relationship between autism and gastrointestinal issues.

Problems With Motor Skills and Coordination

Low muscle tone and delayed development of motor skills can be common in autistic children. This can affect a person’s ability to write, walk, run, play with toys, and take care of themself.

5. Common Coexisting Conditions

Some health conditions are more common in autistic people than in the general population. While these co-occurring conditions aren’t a symptom of autism, they may exist at the same time and make the diagnosis harder.

Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that causes inattention, hyperactivity, or both. Researchers estimate that half of children with autism also have ADHD.

Pica

Pica is a craving to eat nonfood items such as dirt, sand, paint, ice, or hair. Up to 1 in 4 young children with autism have pica. It’s believed that sensory differences may contribute to pica.

Epilepsy

Epilepsy is a brain disease that causes seizures. It’s estimated that between 7 percent and 46 percent of people with autism also have epilepsy. Epilepsy is about five times more common in autistic children with an intellectual disability. In people with autism, seizures most commonly start either in preschool or adolescence. However, about 20 percent of autistic people with epilepsy have their first seizure as an adult.

Hearing and Visual Impairments

Some studies show autism is more common in children with hearing or visual impairments. About 9 percent of children with profound hearing loss and 19 percent of children with visual impairment are also diagnosed with autism.

Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is a mental health condition that causes unwanted, recurring thoughts or repetitive, compulsive behaviors. According to a 2024 study, 11.6 percent of autistic children and adolescents also had OCD. Additionally, 9.5 percent of children with OCD also had autism.

Anxiety Disorders

An anxiety disorder is a mental health condition that causes excessive fear, worry, or nervousness that interferes with daily life. It’s estimated that between 40 percent and 66 percent of school-aged autistic children also have an anxiety disorder.

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