What are autism spectrum disorders?

Autism spectrum disorders (ASDs) are developmental disabilities caused by differences in the brain. Some people with ASD have a known difference, such as a genetic condition. Other causes are not yet known. Scientists believe that ASDs have multiple causes that, acting together, change the ways that people develop. We still have a lot to learn about these causes and how they affect people with ASD.

People with ASD may behave, communicate, interact and learn in ways that are different from most people. Many times there is nothing in their appearance that distinguishes them from others. The abilities of people with ASD can vary significantly. For example, some people with ASD may have advanced conversational skills, while others may not express themselves verbally. Some people with ASD need a lot of help in their daily life; others can work and live with little or no help.

ASDs normally appear before the age of three and can last a lifetime, although symptoms may improve over time. Some children show symptoms of ASD in the first 12 months of life. In others, symptoms may not appear until 24 months or later. Some children with ASD acquire new skills and reach developmental milestones until around 18 to 24 months of age, and then stop acquiring new skills or lose existing ones.

As children with ASD become adolescents and young adults, they may have difficulty forming and maintaining friendships, communicating with peers and adults, or understanding what behaviors are expected of them at school or work . They may come to health care providers because they also have conditions, such as anxiety, depression, or attention deficit hyperactivity disorder, that occur more often in people with ASD than in people without ASD.

Signs and symptoms

People with ASD often have problems with social communication and interaction, and restrictive or repetitive behaviors or interests. People with ASD may also have different ways of learning, moving, or paying attention. It is important to note that some people without ASD may also have some of these symptoms. These characteristics can make life very difficult for people with ASD.


Diagnosing ASDs can be difficult because there is no medical test, such as a blood test, to diagnose them. To make a diagnosis, doctors evaluate the child’s behavior and development. ASDs can sometimes be detected at 18 months of age or earlier. By age two, diagnosis by an experienced professional can be considered reliable.1 However, many children do not receive a definitive diagnosis until they are older. Some people do not receive a diagnosis until they are teenagers or adults. This delay means that there are people with ASD who may not get the early help they need.


Current treatments for ASD seek to reduce symptoms that interfere with daily functioning and quality of life. ASDs affect each person differently, and this means that people with ASDs have unique strengths, challenges, and different treatment needs.2 Treatment plans are often involved with multiple professionals and are tailored to each person.

Risk factors

There is no single cause of ASDs. Many factors have been identified that could increase a child’s chance of having an ASD, including environmental, biological, and genetic factors. Although we know little about the specific causes, the available evidence indicates that the following may put children at higher risk of developing an ASD:

  • Having a brother or sister with ASD
  • Having certain genetic or chromosomal conditions, such as fragile X syndrome or tuberous sclerosis
  • Having had complications at birth
  • Being born to older parents

The CDC is working on one of the largest studies of ASDs in the United States to date. This study, called the Study to Explore Early Development (SEED), was designed to investigate risk factors and behaviors related to ASDs. CDC is doing a study that follows older children who were enrolled in SEED to determine the health status, functioning, and needs of people with ASD and other developmental disabilities as they age. 

What we know about prevelence

CDC estimates that about 1 in 44 8-year-old children have been identified with ASD (or 23.0 per 1,000 8-year-olds). These estimates from the ADDM Network are based on data collected from health and special education records of children living in 11 communities across the United States during 2018. Information was collected on children who were 8 years old because previous work has shown that, by this age, most children with ASD have been identified for services. Research shows:

  • There are large differences between geographical locations
  • Boys were 4 times as likely to be identified with ASD as girls.
  • ASD occurs among all racial, ethnic, and socioeconomic groups. There was no overall difference in the number of Black, White, Hispanic, and Asian/Pacific Islander 8-year-old children identified with ASD. However, at several sites, the number of Hispanic children identified with ASD was lower compared to White or Black children.
  • Among children identified with ASD who had IQ scores available, about one-third (35.2%) also had intellectual disability.

Click here to find out more about autism prevelence estimates.

If you are worried

As a parent, you already have what you need to help your young children learn and grow. CDC has developed materials to help you track your child’s developmental milestones and share progress, or any concerns, with your child’s doctor at all checkups.

Learn more about CDC’s milestone checklists and other materials for parents.

Contact your child’s doctor if you think your child might have an ASD or if you have any other concerns about the way your child plays, learns, speaks, or acts.

If you’re still concerned, ask your doctor to refer you to a specialist who can do a more in-depth evaluation of your child. Specialists who can do a more in-depth evaluation and diagnosis include:

  • Developmental pediatricians (doctors who have received special training in child development and children with special needs).
  • Child neurologists (doctors who treat problems of the brain, spine, and nerves).
  • Child psychologists or psychiatrists (doctors who specialize in people’s mental processes).

You can find a list of English-speaking pediatricians, child psychiatrist and child psychologists in the ESHA Spain business directory 

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