Many adults are living with undiagnosed autism without realising it – these are the seven hiddensigns experts want you to know

From workplace challenges to social exhaustion, Anne Fletcher explores the subtle traits of autism that can remain hidden for decades before a diagnosis.

Words: Anne Fletcher. Images: Shutterstock.

I remember the first time I heard about autism. It was the 80s, and Dustin Hoffman was huge. Then he did Rain Man. It took the world — or at least our corner of the world — by storm. Every adult I knew was talking about it, stopping in the street, in the supermarket. It meant something.

Now, yes, I know Hoffman’s character here was in fact an autistic savant, and this is very different from your typical autistic person. But it was the first I, my parents, their friends, and probably many people in the UK had ever heard of the condition. Fast forward a few years, and I remember a friend explaining more to me.

Picture the scene: you ask someone to post a letter for you. It’s got the address on, and a stamp — you’re just asking them to pop it in the post box down the road on their way to get milk. They return four hours later, having caught two buses across town (and back) to hand deliver the letter to the house in question.

It hadn’t crossed your mind that they would go to those lengths, it was surely obvious that you simply meant to put it in the post box, instead of delivering it themselves? Obvious to you, yes, but not necessarily to them. It’s a mistake few people make in real life, and one you’ve probably never encountered. Unless their condition is particularly impactful, then many women, in particular, will learn how to mask it.

They likely never get to the stage of trekking across town to hand-deliver the letter, learning instead at an early age what is meant by ‘posting’, and many other terms. And so they may manage in society, struggle on, getting by, without the condition ever coming to light. Indeed, the most recent figures show that most autistic people over the age of 40 in the UK are living without an official diagnosis.

Researchers at the Institute of Psychiatry, Psychology & Neuroscience at King’s College London analysed research on UK healthcare data from 2018 and estimated that among autistic adults aged 40 to 59, 91% of men and 79% of women have not received a formal diagnosis. This number increased even more in the older age groups: 96% of men and 97% of women with autism over 60 are thought to be undiagnosed.

In contrast, the estimated that the rate of undiagnosed autism for 20 to 39-year-olds is 52%, and 23% for those under 19. Tim Nicholls, assistant director of policy, research and strategy at the National Autistic Society, said: ‘This research clearly shows what we already know and hear about every day — there are high numbers of undiagnosed autistic adults and going through life without a diagnosis has a major impact on many aspects of their lives.

‘Autism assessments can be the first step to understanding people’s needs and a diagnosis can be life-changing and, in some cases, lifesaving.’

So what do we need to look out for, Dustin Hoffman and unexpected posting trips aside? While every autistic person is different, common signs of the condition include difficulty in understanding social rules and sensory sensitivities.

To better understand how autism may present later in life, Dr Lisa Williams, clinical psychologist and founder of The Autism Service, has shared seven subtle signs of autism that often go unnoticed in adults over 40…

1. Reliance on structure and predictability

‘Older autistic adults who have remained undiagnosed for much of their lives often fall into a set routine, which can make them feel more comfortable and in control,’ explains Williams. ‘Reliance on this can become more noticeable with age, as unexpected changes and disruptions to this routine can trigger stress and anxiety. ‘Signs of a reliance on routine can include extensive planning ahead, sticking to daily habits, and feeling unsettled by spontaneous or sudden changes in plans.’

2. Having specific and obsessive interests

‘It’s not uncommon for anyone with autism to develop deep interests in particular subjects or hobbies, but this can be especially the case for older adults,’ says Williams. ‘This can appear to be a lifelong passion, but if it dominates their free time and tends to be something they talk about almost obsessively, it could be a sign that the person falls somewhere on the autistic spectrum.’

3. Sensory sensitivities

‘Heightened sensitivity to key sensory sources like light, noise, smells and textures can persist into later years for autistic adults,’ notes Williams. ‘Noticeable discomfort in crowded and loud environments or with particular fabrics might indicate sensory processing differences typical of autism.’

4. Struggles with change

‘Change can be especially challenging for older adults who may have undiagnosed autism,’ highlights Williams. ‘Moving house, starting a new job or adapting to new technology can draw out natural anxieties about a lack of predictability and familiarity. Consistent signs of this can be a hallmark of autism.’

5. Difficulty in understanding social rules

‘Unwritten social norms, such as eye contact, small talk, respect for personal space, body language and understanding subtle humour, as just a few examples, can be more difficult to understand for older adults with autism,’ says Williams. ‘People with autism often think differently from neurotypical people and can interpret things much more literally or struggle to pick up on subtle social cues. ‘This may result in feeling out of step in social settings or needing extra time to process interactions, even with years of life experience.’

6. Struggles in romantic relationships

‘Adults with autism may experience challenges in forming or maintaining romantic relationships,’ says Williams. ‘This can include difficulty expressing or interpreting affection, discomfort with physical intimacy, or preferring independence over cohabitation. They often thrive in relationships with partners who are understanding of their needs, communicate openly, and are willing to adapt to their preferred ways of connecting.’

7. Integration difficulties in the workplace

‘While many autistic adults excel in specific roles or tasks, they may struggle with aspects of workplace integration, such as adapting to frequent changes, navigating office politics, or participating in group meetings that feel overwhelming,’ says Williams. ‘However, supportive managers who provide reasonable adjustments, like clear communication or flexibility in work routines, can help them succeed. Without this understanding, autistic employees may face unnecessary stress, conflict, or even unfair disciplinary action.’

For more information about autism diagnosis and assessments, visit the National Autistic Society’s website at autism.org.uk.