What Is Autism?

Get the facts about the signs and symptoms

Autism is a complex neurobiological disorder of development that lasts throughout a person's life. It is sometimes called a developmental disability because it usually starts before age three, in the developmental period, and because it causes delays or problems in many different skills that arise from infancy to adulthood.

The main signs and symptoms of autism involve language, social behavior, and behaviors concerning objects and routines:

Communication -- both verbal (spoken) and non-verbal (unspoken, such as pointing, eye contact, or smiling)

Social interactions -- such as sharing emotions, understanding how others think and feel (sometimes called empathy), and holding a conversation, as well as the amount of time a person spends interacting with others

Routines or repetitive behaviors -- often called stereotyped behaviors, such as repeating words or actions, obsessively following routines or schedules, playing with toys or objects in repetitive and sometimes inappropriate ways, or having very specific and inflexible ways of arranging items

People with autism might have problems talking with you, or they might not look you in the eye when you talk to them. They may have to line up their pencils before they can pay attention, or they may say the same sentence again and again to calm themselves down. They may flap their arms to tell you they are happy, or they might hurt themselves to tell you they are not. Some people with autism never learn how to talk. These behaviors not only make life challenging for people who have autism, but also take a toll on their families, their health care providers, their teachers, and anyone who comes in contact with them.

Because different people with autism can have very different features or symptoms, health care providers think of autism as a "spectrum" disorder -- a group of disorders with a range of similar features. Based on their specific strengths and weaknesses, people with autism spectrum disorders (ASDs) may have mild symptoms or more serious symptoms, but they all have an ASD. This fact sheet uses the terms "ASD" and "autism" to mean the same thing.

What Causes Autism?

What causes autism? Scientists don't know exactly what causes autism at this time.

Much evidence supports the idea that genetic factors -- that is, genes, their function, and their interactions -- are one of the main underlying causes of ASDs. But researchers aren't looking for just one gene. Current evidence suggests that as many as 10 or more genes on different chromosomes may be involved in autism, to different degrees.

Some genes may place a person at greater risk for autism, called susceptibility. Other genes may cause specific symptoms or determine how severe those symptoms are. Or genes with changes or mutations might add to the symptoms of autism because the genes or gene products aren't working properly.

Research has also shown that environmental factors, such as viruses, may also play a role in causing autism.

While some researchers are examining genes and environmental factors, other researchers are looking at possible neurological, infectious, metabolic, and immunologic factors that may be involved in autism. Because the disorder is so complex, and because no two people with autism are exactly alike, autism is probably the result of many causes.