Melanie Sykes described the experience of her autism diagnosis at the age of 51 as “life-changing” and one that helped her make sense of previously unexplainable struggles she had faced. It is also part of a wider trend, with an exponential rise in the number of women being newly diagnosed with autism in adulthood in the past two decades.

Experts say the increase is being driven by a growing awareness that autism is not, as was once the perception, a “male condition” and that there can be subtle differences in how autism presents in females.

Francesca Happé, the director of the Social, Genetic and Developmental Psychiatry Centre at King’s College London, said: “It’s a phenomenon at the moment.” There’s an estimated one in 65 children with autism in Ireland. In Northern Ireland, that figure narrows to almost one in every 20 school-age children having an autism diagnosis. The focus is now on adults. “There’s been a lot more awareness and a lot of women coming for a first diagnosis in mid-life.”

This is reflected in the shifting male-to-female ratio of autism diagnoses. In 1998, 18 per cent of new diagnoses in England were of females, increasing to 23 per cent in 2018. Studies based on active screening of children rather than diagnostic records suggest that the ratio for those meeting current diagnostic criteria is closer to 3:1.

Happé says that diagnostic criteria themselves have been skewed towards identifying autism in males because until recently most scientific studies have recruited only boys and men. “Because we thought there were so many more males than females affected, for neuro-imaging studies females were just seen as noise in your sample,” she said. “In recent years there’s been an active seeking out of women for research.”

From this new body of work, evidence is emerging of subtle differences in how autistic traits present in males and females. “Cognitively, females might have some advantages in terms of memory and mental flexibility which means they’re better able to perform in social situations, in effect masking their autism,” said Hannah Belcher, an autism researcher at King’s College London.

Autism is a spectrum disorder, which is defined by having difficulties with social communication and restricted or repetitive behaviours, activities or interests. It is a neurodevelopmental disorder, meaning that these difficulties would have existed since childhood even if someone is diagnosed as an adult.

Autistic traits appear on a spectrum, meaning that people are affected in different ways and to different degrees. For instance, some autistic people are unable to speak or have very limited verbal communication, while others have sophisticated language skills, but may struggle with taking things literally or find abstract concepts harder to follow.

Autistic people may have difficulty reading other people’s emotions or intentions, which can make socialising difficult to navigate. They may struggle to make friends or sustain friendships. That doesn’t mean that autistic people lack emotion or do not desire friendships and social acceptance, however.

Change to routines or unexpected events can be stressful. Autistic people may prefer to stick closely to a known pattern of behaviour, such as eating the same meal each morning, wearing the same clothes. Some autistic people repeat movements such as flapping their hands, rocking or twirling around and find that these behaviours help calm them down when they are feeling anxious.

Autism is linked to highly focused interests or hobbies. The topic could be something niche like stamp collecting or electricity pylons, or something more mainstream such as environmental activism or fashion. It’s the nature and intensity of the interest that is unusual, not necessarily the topic.

Autistic people may also have sensory sensitivities, such as finding loud noises overwhelming, finding scratchy materials particularly uncomfortable or having an aversion to certain food textures.

An autism diagnosis is made on behavioural criteria and this criteria has broadened over time. This means that autism spectrum disorder is a very diverse group with some needing full-time support and others having specific challenges in certain areas of their lives.

“We also know that this group is more likely to camouflage, possibly due to socialisation pressures to ‘fit in’ with others, and so will attempt to compensate for their autistic traits.”

This does not necessarily mean that the core traits are different – but they may be perceived differently by others. Recent research by Belcher suggests that, for instance, non-autistic people view the social behaviours of autistic women more favourably than they do those of autistic men.

The increasing awareness that autism affects women is set against a huge increase in diagnosis across the board. A recent analysis found that in 1998 just 3,072 people in England were newly diagnosed with autism. By 2018 the figure had risen to 65,665, with the steepest rises in females and adults.

“The main reason for this is that the criteria for diagnosis has changed over time – it has expanded,” said Ginny Russell, of Exeter University, who led the research. “As time has passed, less severe traits have been required.”

“It’s good to remind ourselves that autism isn’t a fixed object – it does morph over time,” she added.

This shift is a point of contention in the autism research community. “Some question the clinical utility of the broadening diagnostic criteria,” said Russell. “For people like Mel [Sykes] it has been personally helpful. It can be an explanation for why people have never fitted in.”

However, Russell said that the broadening of the criteria might mean that a diagnosis was “not that useful” for recommending a clinical pathway because the group is now so diverse.

Some point to the potential risks of failure to diagnose autism, which is linked to a range of other mental health issues, including anxiety. One small study found that 23 per cent of women receiving hospital treatment for anorexia met the diagnostic criteria for autism, although it did not establish whether the women’s social and communication difficulties predated their eating disorder.

Another study, published this year, suggested that women diagnosed with autism in adulthood were more likely than men to have previously been misdiagnosed with personality disorders or other conditions.

Belcher, who was diagnosed at the age of 23, had anxiety as a child and dropped out of school before her GCSEs because of mental health problems. She believes she would have received more support if she had been diagnosed earlier. “The difficulty is that these women are also more likely to have mental health issues, and we think that’s because of the exhaustion from camouflaging and lack of support they’re receiving,” she said.

In Belcher’s experience, autistic women are often told “but you don’t look autistic”, because the image of autism has been biased towards males and children. “Previously we weren’t visible … but with people like Mel Sykes coming out, so to speak, it gives the others courage to do the same,” she said. “This is really positive for raising awareness of different autism presentations.”

This article first appeared in The Guardian on November 19, 2021.