Many late realised autistic people like me struggle with the question of how we can ever know if we are really autistic. Even if we do extensive research, and all the descriptions of the autistic experience and traits resonate with us, we still doubt.

Some of us don’t have access to official diagnosis, and many of us still doubt even when we are diagnosed as autistic. Maybe we’re faking our traits? Are we impostors? Can we really call ourselves autistic if were not 100% sure?

I’m hoping that some of that doubt can be alleviated going back to the basics, and examining what autism actually is, and how its defined and diagnosed.

The tl/dr: there is no hidden neurological dial pointing to “autistic” or “neurotypical”. Autism is defined by the traits. If you have the traits, strongly, and there is no other clear cause, you are autistic.

What is Autism

Autism is a neurological difference. Our brains and nervous systems are different from neurotypical peoples’. Because of this difference, autistic people behave differently and experience the world differently in a particular pattern. Those differences are called “autistic traits”.

Broadly speaking, autistic traits fall in three categories: differences in social interaction, differences sensory perception, differences in how we process information, and set patterns of behaviour.

• Difficulty with making eye contact is a well known autistic trait. That’s an example of a difference in social interaction.
• Many autistic people struggle to concentrate in a noisy environment, which is an example of a difference in sensory perception.
• Autistic people often gain great joy in learning about a topic they are especially interested in, and telling others about it. This is a difference in processing information.
• An example of a set pattern of behaviour is when a person eats exactly the same food every day, prepared in exactly the same way.

This is a gross simplification of the patterns of autistic behaviour and experience. I’ve included a link to more nuanced approaches at the end of this article.

Autism was first identified when we realised that many people have this broadly similar pattern of behaviour and experience. We know that autism is caused by our brains and nervous systems being different, but that brings up several questions.

• How is an autistic person’s brain different from a neurotypical person’s?
• What causes this difference?
• What is the result of this difference?

We can only answer the last of these three questions. The result of our neurological difference are the autistic traits. Since we don’t know exactly what the differences are on a biological level, and we don’t know what causes them, the only way to diagnose autism is through identifying autistic traits.

How is an autistic person’s brain different?

Although we know that there are biological differences between autistic and neurotypical people’s brains, we can’t use a brain scan, or a blood test, or a genetics test to diagnose autism.

Scientists have detected areas of difference in some autistic people’s brains, that show up on brain scans, but none of these differences are present in enough autistic people, and not present in enough neurotypical people, for us to be able to use them as a diagnostic tool.

Similarly, while an autistic person is much more likely to have an autistic child, the genetic aspect of autism is complex. There is no single “autism gene”. Instead, there is a complex pattern of genes that, when they appear together, make it much more likely that a person is autistic.

Once again, the pattern is not clear or predictable enough for us to be able to use the presence of those genes are a diagnostic tool. Many autistic people don’t have those genes. Many neurotypical people do.

There are many theories of how autism manifests in the brain. Some examples are the “intense world theory”, monotropism, signalling imbalance, and connective theory among others.

The fever analogy

There are many theories about what causes autism. None of them explain all aspects of autism, or apply to all autistic people. The autistic traits could be caused by any number of neurological differences.

Based on our current understanding of autism, the relationship between the autistic traits and the underlying biological cause of those traits, is similar to the that of fever.

We detect a fever by measuring a person’s body temperature. A fever is defined as having a temperature that’s higher than normal.

A fever might be caused by many different things. For example, a person might have a viral infection such as Covid 19, or bacterial infection such as salmonella, or an inflammatory condition such as rheumatoid arthritis. Many things can cause a fever.

A fever is not defined by its underlying cause, but the detectable aspect: having higher than normal temperature.

Autism is like fever. It’s not defined by its underlying cause, but by its detectable aspect: the autistic traits.

How is autism diagnosed?

Autism is defined by its traits.

If you have:

• many of the autistic traits
• you have those traits strongly
• there’s no other clear cause for those traits

you are, by definition autistic.

That’s what autism means. There is no secret neurological dial that points to “autistic” or “neurodivergent”. There is only the presence, or absence of traits.

What are autistic traits?

Some of the autistic traits are listed in official documents like the DSM5 and ICD11 diagnostic criteria for autism. Many autistic traits are not included in those documents.

Note that the DSM5 and ICD11 diagnostic criteria for autism are not used to determine whether or not a person is autistic. They are tools to determine whether a person is disabled enough by their autism to qualify for accommodations and disability allowances. A person can be autistic, and not meet the criteria defined in these documents, if they don’t meet these documents definition of disability.

Some autistic traits are not included in these documents because they don’t occur often enough to be useful when diagnosing a person.

Some traits are not included in the official criteria because of the bias of autism science, which is based on how autism presents in a small subset of the autistic population: male, white, middle-class children in Western cultures.

Examples of autistic traits that are not included in the official criteria:

• Many autistic people are trans, non-binary, or have other non-standard experiences of their gender identity.
• Autistic people often don’t recognise the conventions of social hierarchy, and may not change the way they speak or behave to match their status in the eyes of others.
• Autistic people often form emotional attachments to inanimate objects.

There is no autistic trait that all autistic people have. There is no autistic trait that no neurotypical people have.

For example, a well known autistic trait is a difference in making eye contact. There are autistic people who don’t have this trait, or who have taught themselves to hide this trait. There are neurotypical people who have this trait — they have differences in how they make eye contact, but they are not autistic.

No single autistic trait can prove, or disprove, that a person is autistic.

Autism is diagnosed by a person having many autistic traits, having them strongly, and there being no clear alternative explanation for those traits.

Autistic traits can be tested for using questionnaires, by being interviewed and observed by a trained professional, or by the person themselves doing research on autism, reflecting on their own experience, and spending time with other autistic people to see whether their share experience makes sense.

It takes training and experience to identify autistic traits in another person. This is because autistic traits are differentiated from symptoms of other conditions based on their internal experience, and not by their external presentation.

This is why informed autistic self diagnosis is just as valid as professional diagnosis by a professional.

What other conditions can look like autism?

Many autistic traits are symptoms of the trauma of being autistic. Autistic people have had their needs ignored or misunderstood from birth, causes long lasting trauma. Autistic people also often have very sensitive nervous systems, and so are far more likely to experience anxiety and stress disorders.

For this reason, all the mental health conditions and personality disorders that are associated with trauma have symptoms that overlap with, or look very similar to, the autistic traits.

Examples are cPTSD (Complex Post Traumatic Stress Disorder), PTSD, Borderline Personality Disorder and Narcissistic Personality Disorder, all of which are related to trauma.

Other conditions that can look like autism are Bipolar Disorder, Generalised Anxiety, and Social Anxiety. Of course, it’s also possible for an autistic person to have one or more of these conditions as well as autism.

It can be very difficult for an autistic adult to be correctly diagnosed as autistic. While there are benefits to having an official diagnosis, such as access for accommodations for work and school, official diagnosis might not be necessary in order to know whether or not you are autistic.

For more information on other aspects of autism, such as what is meant by the autistic spectrum, differences in empathy, the difference between autism and social anxiety, how to manage anxiety and autism, and what is meant by neurodivergent supporting therapy, here is a curated list of resources for autistic adults.