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What is the difference between low-functioning and high-functioning autism? Let's take a deeper look.

Autism is hard to define. Often described as a life-long neurological disorder that can cause disability and interfere with daily functioning in all sorts of ways, there is no question that it is a spectrum — something its official diagnostic label of "autism spectrum disorder" very much acknowledges.

This means that no two autistic people are the same, but isn't that true for people who aren't autistic, too? Well, not exactly.


Autism is a descriptor for brains that are wired differently than those of neurotypical people (non-autistic people), but that's where things get really interesting. Some studies have found that autistic folks have fewer brain connections, while others have come to the conclusion that they actually have more. More recent research in which people on the spectrum took part in functional MRI scans revealed that both can be true. While the brains of neurotypical people tend to be very much alike, autistic brain wiring is unique to each person. Autism shows up in brain scans, then, but in very different ways.

It may be because of this that, any time I think or write about autism, I'm reminded of something a transgender man — who also happens to be autistic, but that is not relevant to the story — once told me. How did he realize he was a man? What exactly is a man? When I asked him these questions, he told me that he really had little idea how to define "man". He just knew he was one. Looking at the diagnostic criteria for autism spectrum disorder, you'll see that autism can manifest itself in very different ways. Just like there's no one unified concept of what it means to be a man, there's no one set of characteristics that universally denote an autistic person. 

So, what's the difference between low-functioning and high-functioning autism?

Low-functioning autism and high-functioning autism (also called severe or mild autism), are terms you'll come across all the time when reading stuff about autism or discussing the spectrum with people you meet. What do they really mean? Well, the very long document used to diagnose mental disorders in the US, the fifth edition of the diagnostic and statistical manual of mental disorders (DSM-5 for short) actually offers some guidelines.

They have divided autism into three "levels":

  • At level 1, an autistic person will "require support" to function optimally. They may face social struggles and come across as weird if they don't get this support, and have difficulty adjusting to change or multitasking. 
  • At level 2, an autistic person requires "substantial support" to function well. The fact that they're not neurotypical is pretty obvious to anyone who interacts with them, and they experience significant distress when faced with change or when they don't have access to their coping behaviors. 
  • At level 3, an autistic person needs "very substantial support" in the neurotypical world. They may not be able to use words to communicate, or in a very limited way, and may rely on augmentative and alternative communication devices. Their behavior is considered highly inflexible and adapting to change is incredibly hard. 
So, looking at that, it seems quite obvious — someone with level 1 autism would be considered high-functioning, or would be considered to have "mild" autism. This person may be told they don't "seem autistic" quite a bit. Someone with level 3 autism would, on the other hand, be deemed "severely autistic" or "low-functioning". 

In other words, a lot of this really refers to how well the person in question is able to come across as neurotypical; how obvious it is, to outsiders and those close to the person, that they are autistic. 

The problem? The same person who is brilliant at their job — which aligns closely with their passions — and comes across as quirky but funny and creative may completely melt down, unable to function, in an environment less suited to their needs. They may panic, lose their speech, and sit on the floor. The same person non-verbal person may come across as "being in their own world"... until they have access to augmentative and alternative communication devices, which allow them to communicate brilliantly in writing. 

The same person may have the characteristics of level 1 autism on one day or in one environment, and those of level 3 another day in another context. Getting the right support in place means that someone who would be "low-functioning" without that support is now "high-functioning", while taking it away will do the opposite. 

Functioning labels are, as such, fairly arbitrary. Many in the autistic community greatly dislike them. To understand why, you may consider that a non-autistic person who functioned perfectly suddenly becomes "low-functioning" when they develop major depressive disorder — or when they're placed in a totally alien culture where they don't speak the language. This "low-functioning" state isn't necessarily for life; it can change with treatment or a changed context.

A better question to ask than "is this person high- or low-functioning?" would be, then, "What can I do to help meet this person's needs so that they can feel comfortable and can accomplish their goals?"

  • American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA
  • Photo courtesy of SteadyHealth

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