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Written by Ada’s Medical Knowledge Team

Updated on

What is autism?

Autism, or autism spectrum disorder (ASD), is a developmental disorder that affects how people communicate and interact with others, as well as how they behave and learn. 1

There is no one definition of autism, as people with autism do not all experience the same symptoms or at the same severity. Autism is a spectrum disorder, which means that people can experience a wide range of symptoms at a varying degree of severity. 2

The Centers for Disease Control and Prevention has identified that one child in 59 in the United States has an autism spectrum disorder. 1 to 2 percent of American children have received a diagnosis of autism spectrum disorder. Autism occurs in people of all ethnicities and is around four times more common in boys than in girls. 3

Symptoms of autism generally appear by the time a child is two years old. Autism cannot be cured but therapies and support services can help a person with autism improve symptoms. 2 4

Symptoms of autism

Autism is a spectrum disorder, which means that the signs and symptoms vary from person to person. Some of the more common symptoms of autism include: 5

  • Not making eye contact
  • Delayed speech and communication skills
  • Relying on rules and routines
  • Becoming upset by changes to routines
  • A narrow or obsessive range of interests
  • Unexpected reactions to tastes, sounds, smells, sights and touch
  • Difficulty understanding other people’s emotions
  • Engaging in repetitive behavior such as flapping hands or rocking

Symptoms of autism spectrum disorder are usually noticeable, and can be diagnosed by a medical professional by the time a child is two years old. Autism is diagnosed more frequently in males than females. In girls, symptoms of autism may be masked or missed, and the disorder is thought to be underdiagnosed. 6 7 8 9

Read more about Signs of Autism »

Autism spectrum disorder is connected with various other conditions.

Learning disabilities and autism

Between 40 and 55 percent of people with autism spectrum disorder also have a learning disability. The impact of learning difficulties on a person can range from needing support in school to needing support in all aspects of their daily life. 10 11

Anxiety and autism

Anxiety and anxiety disorder are often found in people with autism spectrum disorder. Anxiety can be increased by changes to routine or confusing social situations. This anxiety can be expressed as: 12

People with higher functioning levels of autism spectrum disorder seem more likely to have anxiety and anxiety disorders as well.

Gastrointestinal problems

Up to 70 percent of people with autism spectrum disorder also have some form of gastrointestinal condition, such as diarrhea or gastritis. Many people with autism also develop intense preferences for certain foods. 13

Where gastrointestinal problems cause pain and distress, this can cause the person to display frustrated and/or challenging behavior. If you are worried about any gastrointestinal symptoms, you can try using the Ada app for a free assessment.

Chronic constipation

If a person with autism has chronic constipation, there could be a lack of fibre in their diet. There may be physical causes, such as problems in the gut or metabolism that should be referred to a medical professional if constipation continues.

Chronic diarrhea

Chronic diarrhea can be caused by food intolerances, such as to lactose or gluten, in which case it is generally treated by restricting the diet. Chronic diarrhea should be assessed by a medical professional. Other causes of diarrhea include: 14

Gastroesophageal reflux disease

Gastroesophageal reflux disease (GERD) occurs when stomach contents, including stomach acid, leak into the esophagus. This causes irritation and the burning sensation known as heartburn. Symptoms can be eased with medication such as antacids, eating smaller meals or avoiding certain foods. A medical professional can discuss causes, prevention and treatment. 15

ADHD and autism

Autism spectrum disorder and ADHD (attention deficit hyperactivity disorder) can be confused due to similar symptoms, such as:

  • Inability to focus
  • Impulsivity
  • Hyperactivity

Autism is a developmental disorder, whereas ADHD is a biological brain condition that is notable for a lack of attention and patterns of hyperactive and impulsive behavior. 16 17

One study showed that 20 percent of children with autism are initially diagnosed with ADHD. This delay in making the appropriate diagnosis of autism also delays interventions such as behavioral therapy and skills training. 18

Pervasive developmental disorder not otherwise specified (PDD-NOS)

Pervasive developmental disorder not otherwise specified (PDD-NOS) is a condition now considered part of autism spectrum disorder by the DSM-5 19. Symptoms of PDD-NOS have significant overlap with ADHD.

PDD-NOS can be given as a diagnosis for a developmental disorder that does not also meet the criteria for a named developmental disorder, such as autism, Asperger syndrome or Rett syndrome. PDD-NOS is likely to be the diagnosis where a person has:

  • Impairment in social interaction
  • Difficulties with communication
  • A narrow range of interests
  • Repetitive behaviors

Sleep disorders and autism

Difficulty sleeping is common among children and teenagers with autism spectrum disorder. This may be caused by an underlying medical issue, such as gastrointestinal distress or sleep apnea, or poor sleep hygiene and bedtime routines. 20

Epilepsy and autism

Around 20 to 38 percent of children with autism spectrum disorder will have developed epilepsy by the time they become adults. Children who develop epilepsy alongside autism are at a higher risk if they also have a learning disability. The link between epilepsy and autism is thought to come from shared underlying causes. 21 22 23

Read more about Seizures »

Fragile X syndrome and autism

Fragile X syndrome is a genetic development disorder which causes learning disability. The extent of the learning disability can range from mild to severe. People with Fragile X syndrome have an increased risk of also developing autism. 24 25

Tuberous sclerosis complex and autism

Tuberous sclerosis complex (TSC) is a rare genetic disorder that causes benign tumors to form in various organs, particularly the brain. Tumors in the brain can lead to seizures, developmental delays and learning difficulties. One study found that approximately 1 percent of children with autism also have tuberous sclerosis complex. 26 27

Asperger syndrome

People with Asperger syndrome are generally considered to be on the higher functioning end of the autism spectrum. It is a type of autism and is a lifelong condition.

Someone with Asperger syndrome may not be diagnosed until later in childhood or adulthood, as people with the condition often have excellent language skills. Signs that someone has Asperger syndrome can include: 28 29

  • Narrow range of interests or obsession with certain topics
  • Difficulties with social situations and communication with others
  • Places high value on rules and routines

Read more about Asperger Syndrome »

Causes of autism

It is unclear what causes autism, though scientists believe genetics and environment are involved.

Around 85 percent of people with autism spectrum disorder can be classed as idiopathic, meaning the cause is not known. The remaining 15 percent of people have secondary autism spectrum disorder, where a specific cause can be identified. 30

Genetic causes of autism

In up to 25 percent of people with autism spectrum disorder the condition is thought to have a genetic cause. Over 100 genes, many of which concern brain development, may be involved in causing autism. 31 32 33

Good to know: Not everyone with the identified genetic mutations has autism, and not everyone with autism has genetic mutations.

Autism can run in families, although it is unclear why. The brother of a child with autism has a 7 percent chance of developing autism, with an additional 7 percent chance of developing less severe autism spectrum symptoms. The sister of a child with autism has a 1 to 2 percent chance of developing autism plus the additional chance of less severe autism spectrum symptoms. 30 31

Other genetic disorders, such as ADNP syndrome, can cause autism. 34

Medications taken during pregnancy

Valproic acid is used to treat seizures, mania in people with bipolar disorder, and to prevent migraine headaches. Taking valproic acid during pregnancy increases the risk that the child will be born with serious birth defects and that the child will develop an autism spectrum disorder. 35 36

Thalidomide is used to treat a type of cancer called multiple myeloma. It is well known that thalidomide carries a risk of severe birth defects when taken by a person who is pregnant. Thalidomide can also be transmitted to a fetus through semen. Contact with thalidomide before birth increases the risk a child will develop autism spectrum disorder. 37 38

Misoprostol is used to prevent ulcers. It can also be used to induce labour and, in high enough doses, terminate pregnancy in its early stages. There is some evidence to suggest that misoprostol use in the first trimester of pregnancy could cause autism spectrum disorder. 39


When a pregnant person is exposed to the rubella virus during the first trimester, the fetus has a high chance of developing congenital rubella syndrome (CRS). This condition can cause deafness, microcephaly, congenital heart disease and learning difficulties. Congenital rubella syndrome is also associated with higher than usual incidences of autism spectrum disorder. 40 41

CRS is very rare in the United States because of its policy for universal immunization against rubella. A study estimated that over 1,000 cases of autism spectrum disorder were prevented by rubella vaccination in the U.S. between 2001 and 2010. 42

Older parents

Children born to older parents are more likely to develop autism, the risk heightening with the parents’ age. The risk increases significantly for each additional 10 years in maternal and paternal age. 43 44

Birth spacing

A study by the Centers for Disease Control and Prevention found a connection between autism spectrum disorder and the amount of time between births for each mother. The study found that children who were conceived less than 18 months or more than 59 months (4 years and 11 months) after the previous birth were more likely to develop autism. 45

Autism and vaccines

There has been extensive research on vaccines and autism, and all scientific evidence indicates there is no link between autism and vaccines. 46 47 48

Diagnosis of autism

In the DSM-5 19, autism spectrum disorder now covers conditions that used to be classified separately: 5

  • Asperger syndrome
  • Autistic disorder
  • Pervasive developmental disorder not otherwise specified (PDD-NOS)
  • Childhood disintegrative disorder

A person needs to meet all DSM-5 19 criteria to receive a diagnosis of autism spectrum disorder. These criteria include: 49

  • Persistent difficulties in social communication and social interaction in many contexts
  • At least two examples of restricted interests or repetitive behavior
  • Signs must have been present in the early years of life
  • Symptoms cause significant problems in social, working or other functioning
  • Symptoms cannot be explained by other learning or developmental disorders

Some diagnostic tests that may be used to screen for autism spectrum disorder include: 30 49

  • M-CHAT-R (Modified Checklist for Autism in Toddlers, Revised)
  • CARS (Childhood Autism Rating Scale)
  • GARS (Gilliam Autism Rating Scale)
  • ABC (Autism Behavior Checklist)
  • Social Communication Questionnaire
  • ADOS (Autism Diagnostic Observation Schedule)
  • ADI-R (Autism Diagnostic Interview-Revised)

A diagnosis of autism spectrum disorder will be accompanied by an assessment of severity level, which can determine how much support a person will require.

Diagnosing autism in young children

Some children with autism spectrum disorder display signs within the first few months, others after 24 months old. Up to 90 percent of children with autism display signs before two years of age, but most are diagnosed between the ages of three and five. Some children may develop according to normal patterns but stop developing around 18 to 24 months or lose skills they had already developed. 5

It may be helpful to keep a diary of behaviors, habits and incidents about a child with suspected autism. Record what happened where and anything notable that occured before the incident. 50

The American Academy of Pediatrics recommends reviewing children’s development at all early-years health checks and screening specifically for autism spectrum disorder at the 18-month and 24-month checks. 51

If autism spectrum disorder is suspected, other health professionals will carry out an assessment. These can include: 2 24

  • Developmental pediatrician
  • Psychologist
  • Neurologist
  • Speech therapist

Blood and hearing tests may also be carried out to eliminate other potential causes for the symptoms, such as: 2 52

  • Genetic disorders which can affect development
  • Lead poisoning, which can can cause developmental and behavioral problems
  • Hearing difficulties, which may explain a lack of response

Diagnosing autism in older children and teenagers

Children with less severe forms of autism spectrum disorder may find their symptoms first becoming noticeable at school. For example, a child may find it difficult to form friendships or recognize social cues like sarcasm or jokes. 2

Schools will communicate with parents or carers and may perform an initial evaluation, or recommend visiting a health professional.

Diagnosing autism in adults

Some people do not receive a diagnosis of autism spectrum disorder until adulthood. This can be due to complicating factors, such as the person being on the higher functioning end of the autism spectrum, having other disorders or being misdiagnosed. People with autism can be misdiagnosed with ADHD, obsessive compulsive disorder, depression or anxiety. 53 54

If autism is suspected in an adult, a doctor should refer the person to a psychologist, psychiatrist or neuropsychologist who has experience with autism spectrum disorder. A diagnosis of autism may be reached after taking a history of the person’s life and interaction with others, as well as potentially talking to family members who may remember details of the person’s early development. 2

A diagnosis of autism as an adult can provide the person with an explanation for previous difficulties and offer the opportunity for self-understanding and access to services.

Genetic testing

Where there is a family history of autism spectrum disorder or physical evidence of another genetic disorder present, gene testing or chromosome analysis may be carried out. 30

Increase in autism diagnoses

More people are being diagnosed with autism spectrum disorder. However, a variety of factors may be affecting the rate of this increase:

  • More awareness of autism among caregivers leading to more referrals
  • Broader diagnostic criteria
  • Better awareness of diagnostic criteria among medical professionals

There may also be a genuine increase in the number of individuals with autism. However, at present, it is unclear what is behind the statistics. 55

Treatment of autism

There is no standard treatment for autism spectrum disorder. However, there are therapies available which aim to minimize the symptoms of autism and allow the person to function as well as they can.

Intervention and treatment can improve external symptoms and how a person copes with sensory and perception differences. However, how someone processes sensory information such as sounds and smells will always be different to people without the condition. 56

Although treatment, particularly behavioral therapy and skills training, is most effective when started young, any person at any age can benefit from appropriate treatment. Which treatments are appropriate will depend on the person, what they have difficulty with and the severity of their symptoms. 57

Early intervention for autism

In the U.S., early intervention services are available for children up to three years old with developmental disorders, including autism spectrum disorder. These services focus on: 58 59

  • Language development
  • Help with walking and coordination
  • Interacting with others
  • Recognizing and managing emotions

Managing autism

There is no cure for autism spectrum disorder. However, people with autism can learn coping skills to help them function better on a day-to-day basis. Carers and others who interact with people with autism can also help by managing their own behavior and environment.

Therapy for autism

Therapy for autism spectrum disorder aims to decrease unwanted behaviors and increase wanted behaviors. There are various types of therapy available. The most appropriate will depend on the needs and symptoms of the person with autism. A medical professional will be able to offer guidance on which are likely to provide most benefit.

Many therapies involve the whole family, so that family members can learn how to support and help the person with autism. In young children, effective interventions should involve around 25 hours a week of active engagement. 20

Therapies for autism spectrum disorder include: 20 57 58

  • Cognitive behavior therapy (CBT): Helps people recognize the connection between thoughts, feelings and behaviors
  • Behavioral management therapy: Uses various techniques to teach skills which improve social skills and reduce problematic behaviors
  • Occupational therapy: Helps with skills, such as getting dressed or skills needed for employment
  • Social skills training: Can help children cope with conversations and other social interactions

Speech therapy for autism

Many people with autism spectrum disorder experience delays in learning to talk, with up to 50 percent being nonverbal. Being able to communicate by speech by the time a child goes to school has been linked to more positive outcomes as the child grows into adulthood. Early intervention is, therefore, important. 60

Speech-language therapy can help a person with autism express needs, desires and feelings. It can also improve a person’s vocabulary and speed of speech. 61

Managing challenging behaviors

If a person with autism spectrum disorder displays challenging behaviors, there are various courses of potential action to take: 62

  • Have the person tested to check for medical problems that could be causing distress
  • Behavioral therapy
  • Reward positive behavior
  • Communicate simply, to minimize frustration
  • Reduce sensory overload
  • Offer cues to redirect behavior such as verbal or gentle physical instruction
  • Provide relaxation opportunities
  • Be consistent and encourage others do the same

Some challenging behaviors can be mitigated by allowing the behavior, but changing an element to make it more socially acceptable. If a person smears feces because they enjoy the sensation, replace the feces with a substance such as Play-Doh or cornflour mixed with water. With pica, inappropriate items can be replaced with something edible and nutritious. 63 64

Managing repetitive behavior in autism

Repetitive behaviors such as hand flapping or rocking may help a person with autism spectrum disorder. However, some repetitive behaviors, such as head banging, could cause the person harm. Other behaviors may cause distractions, such as in school or can be problematic if engaged in often to block out external sensory input.

Ways to manage unhelpful repetitive behavior include: 65 66

  • Behavioral therapy
  • Replacing harmful activities with safer activities
  • Change the environment to reduce distressing sensory input
  • Introduce other forms of stimulation, such as calming activities

Using visual cues to manage autism

People with autism are often highly reliant on routine. A visual timetable that shows what is going to happen during an activity, outing or a day can provide reassurance and prevent stress.

Pictograms and simple instructional diagrams in soft colors can provide information to people with autism spectrum disorder. Such signs can indicate what room a person is in, or how to operate an appliance or window.

Visual supports can also provide a way to communicate for people with autism who are nonverbal. Cards of various colors or with simple pictograms can indicate a need, desire or mood. 67

Toys for autism

People with autism spectrum disorder process sensory information, such as touch, sight, taste, sound and smell, differently from people without the condition. Certain toys can provide sensory feedback and, while not a treatment, may help a person with autism focus or feel relaxed. 68

Examples of such toys include:

  • Fidget toys
  • Stress balls
  • Bubble wands or machines
  • Sorting and matching games
  • Toy trains
  • Jigsaws
  • Tactile books
  • Construction bricks

Autism-friendly spaces

As social awareness of autism spectrum disorder grows, more public places accommodate people with autism. This can include: 69 70 71

  • Relaxed theatre performances with reduced noise and light levels, and more freedom to move around
  • Specific museum and gallery visiting hours with dimmer lights, fewer people and break areas
  • Autism-friendly times at shopping malls and supermarkets, with fewer people and no background music

Medication for autism

There are no medications that can cure autism spectrum disorder, but some medications may help ease symptoms. Medication is often used to manage a behavior if it threatens to cause harm to the person, such as head banging or slapping.

The FDA has approved aripiprazole and risperidone for use in autistic teenagers and children older than five years old. These medications can reduce hyperactivity and repetitive behaviors. 72 73

Other medications that can be used to treat some symptoms of autism include: 74

  • Antidepressants, including tricyclics and SSRIs: Can reduce anxiety, irritability and aggression
  • Anti-anxiety medication: Can reduce anxiety and panic
  • Stimulants: Can help increase focus for people with less severe symptoms

Treating gastrointestinal problems in autism

It is common to find gastrointestinal problems in people with autism spectrum disorder. Treatment involves diagnosing and treating the underlying issue which is causing the gastrointestinal distress.

Exclusion diets, such as not eating gluten or casein, should not be used unless the person has a specific gastrointestinal problem, and dietary changes are recommended by a doctor. A large study found that, on the whole, children with autism that are given vitamin supplements do not need these supplements and may develop too-high levels of vitamins such as vitamin A and folate. 75 76

Autism prognosis

Autism spectrum disorder is a lifelong condition with no cure. However, intervention and therapy, particular when begun early in life, can equip a person with autism with more life and emotional skills to help them manage.

Depending on where a person fits on the autism spectrum, they may be able to live independently. A small number of people with autism go on to take university courses. A person towards the lower end of the autism spectrum may need lifelong help with daily tasks. 77

Employment may present a challenge for adults with autism. People towards the higher functioning end of the spectrum may need adjustments to the work environment, such as lights that do not flicker or a quiet space to work in. Some people towards the lower functioning end of the autism spectrum may never be capable of holding down a job. Types of employment that may be suitable for people with autism include: 78

  • Computer programming
  • Accounting
  • Photography
  • Mechanics and engineering
  • Sorting and assembly work

Autism FAQs

Q: How do I know if my kid has autism?
A: There are many different signs that a child might have autism. It is a spectrum disorder, meaning that the symptoms differ from one person to another and vary in severity. There are some common signs, such as avoiding eye contact, finding social interactions difficult, being reliant on routines and getting upset at minor changes or certain smells, tastes, sounds or lights. Parents are often the first people to notice symptoms, but a diagnosis can only be made by a team of experienced specialists.

Q: Are autism rates going up?
A: The number of people being diagnosed with autism spectrum disorder is increasing. However, it is unclear whether this is because there are more people with autism or whether parents, caregivers, schools and doctors are more aware of autism symptoms. This can lead to more people with autism being diagnosed, whereas, in the past, they might not have received a diagnosis.

Q: Are autism and ADHD related?
A: Autism and ADHD share some symptoms. Some people with autism are misdiagnosed with ADHD before receiving the correct diagnosis. Autism and ADHD are different conditions, though people with both can display fidgety behavior, struggle with social skills, react unusually to sensory input and experience outbursts due to frustration. See the section on ADHD and autism.

Q: Are autism and Asperger syndrome the same?
A: Asperger syndrome is a condition that is classified as an autism spectrum disorder. Autism is a spectrum disorder, meaning that people can have autism but show different symptoms of differing severity. People with Asperger syndrome are generally towards the higher functioning end of the autism spectrum. See the section on Asperger syndrome.

Q: Can autism be cured?
A: There is no cure for autism. It is a lifelong condition. However, with appropriate intervention a person with autism spectrum disorder can learn to manage their behaviors and emotions, and have a better quality of day-to-day life. See the section on treatment.

Q: What diet should someone with autism and gastrointestinal problems have?
A: It is common for people with autism to experience gastrointestinal problems. Discomfort can cause distress and difficult behavior, prompted by the underlying gastrointestinal medical condition. A doctor should be consulted to find the underlying cause. (See the section on gastrointestinal problems.) No particular diet has been shown to affect symptoms of autism itself.

Other names for autism

  • Autism spectrum disorder
  • ASD