Can a Person Develop Autism After Early Childhood?

Autism spectrum disorder (ASD) is a form of neurodivergence people are born with; you cannot develop it later in life. However, many autistics go undiagnosed throughout their childhood and only learn they have autism in adulthood.

The Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) states that autism "symptoms must be present in the early developmental period." There is no official diagnosis of late-onset autism.

As for why autism may not be recognized in childhood, the DSM-5 notes that symptoms may not be obvious "until social demands exceed limited capacities, or may be masked by learned strategies in later life."

This article discusses how a diagnosis of autism in adulthood does not mean a person has developed autism or has late-onset autism. It explains how autism can go undetected and how to get assessed for autism as an adult.

Late Recognition of Autism

There is a difference between a late recognition of symptoms and late onset of symptoms.

Autism is a wide spectrum and many children with level 1 ASD can go undiagnosed until the demands of life exceed their capacity to function. Many people with autism get by in society by masking—or hiding their autistic traits—to fit in with others.

Children are often diagnosed with autism before the age of 3. However, it's not unusual for a child with with level 1 ASD, or so-called high-functioning autism, to go undiagnosed until social challenges arise in school. Some people are not diagnosed with autism until adulthood.

A late diagnosis of autism does not means symptoms suddenly developed, though. Rather, the symptoms are so subtle that it's only with time that their impact becomes obvious.

Autism masking is particularly common among girls, who are more likely to, for example, follow others' lead or become very passive in order to avoid being identified as "different."

Is There an Age Limit for Autism?

Older children, teens, and adults do not suddenly develop autism. Autism is a neurotype some people are born with that causes behavioral and social communication problems.

According to the Centers for Disease Control and Prevention, one in 44 children are diagnosed with autism. However, as a diagnosis, autism has only been around since 1980 and a growing number of adults are being diagnosed late in life.

Research into later-in-life autism diagnoses shows that adults with autism were acutely aware of being different as children and reported peer rejection and isolation.

Can You Develop Autism As an Adult?

If you know an adult who has suddenly, out of the blue, developed autistic traits, it is unlikely they have acquired autism after a period of normal development.

People who appear to suddenly behave in an "autistic" manner may have developed any one of a number of other mental health issues, some of which do most commonly appear in early adulthood.

Autism-like behaviors may result from a wide range of disorders, including:

• Generalized anxiety disorder
• Obsessive-compulsive disorder
• Social phobia and other phobias

These are serious disorders that have a significant impact on an individual's ability to function effectively, make or keep friends, or hold a job, and they should be treated. But they are not autism.

What Is Autistic Regression?

Autistic regression is a loss of acquired communication or social skills. Research shows some children appear to regress into autism while others either show signs of autism in infancy or "plateau" in their development.

Studies looking at the younger siblings of children with autism in their earliest months are discovering that subtle regression is quite common. While parents may notice issues such as loss of language or eye contact, researchers note small losses in the areas of motor skills and response to social cues.

Such regression typically occurs before age 3. According to one study, around one third of children with ASD experience this regression, and the average age of onset is around 20 months.

At present, no one knows exactly what causes regression, but according to developmental-behavioral pediatrician Paul Wang, “We understand now that regression is common. It starts early, and it can affect many different developmental skills."