The other day a man waved at Stanley Chow, and went over to him. “I said: ‘Have we met before?’ Which is kind of the last thing you want to say.” It happens a lot – he finds it hard to remember new people’s faces. “Anyone I’ve spoken to once or twice I do forget quite instantly,” he says. “If I meet someone new, I’ll make a point of following them on Instagram or Facebook so their face becomes ingrained in my memory somehow.”

Around six months ago, a friend phoned Chow to complain he had “blanked” a mutual friend, but the 48-year-old illustrator just hadn’t recognised him. “That unsettled me for a few weeks.” Now, he says, “I always make an excuse, like: ‘Since Covid I can’t remember faces as well as I could.’” He’s not plucking that idea out of thin air. He says he has always had a small degree of face blindness – where people have difficulty recognising or remembering faces – but he believes the Covid infection he got in early 2021 made it worse.

Face blindness, or prosopagnosia, has been raised as a possible symptom of long Covid. Last month, researchers at Dartmouth College in the US published a case study on Annie (a pseudonym), who had developed prosopagnosia since having Covid, to the extent she couldn’t recognise members of her own family. The study is extremely limited – Annie is just one person, and she wasn’t given an MRI scan to rule out other causes of prosopagnosia, such as stroke (Covid itself raises the risk of stroke).

The researchers are still at an early stage. However, there is another person who has claimed they have post-Covid prosopagnosia they want to work with, says Marie-Luise Kieseler, a doctoral student and lead author of the study, and two others who have been in touch. “We heard from another man who is not experiencing face blindness, but face distortions,” she says.

Based on responses to a survey she did, “we do think there are lots of people who have some sort of visual problems after contracting Covid-19. Some people have reported colour vision changes. We’ve heard from people who have trouble with navigation, recognising streets that are supposed to be familiar to them and losing their way when travelling.” One woman told Kieseler she has had a lot of visual distortions, including seeing shadows as trenches. More people with long Covid reported problems keeping track of characters in TV shows than people who had recovered from the virus, she says.

Prosopagnosia is a rare condition, and most of the cases are acquired through some sort of brain injury or diseases such as encephalitis or Alzheimer’s, but some people are born with it. Haaris Qureshi, an IT and data technician, has had it – alongside dyspraxia, which affects motor skills and coordination – for as long as he can remember. “I’ve always struggled in social situations to be sure if I know someone.” It’s annoying, rather than debilitating, he says, but he does sometimes go out of his way to avoid people, rather than risk blanking them.

If he has known or worked with someone for a while, he will remember them. “But even then, with someone I know very well, if I see them in the context I’m not expecting them, I won’t recognise them.” When we speak, Qureshi, 28, is on a work training course and is meeting new people; he remembered one of his workshop partners by the colour of the tracksuit they were wearing, but they were wearing a different-coloured one the next day and he couldn’t pick them out. “These are the things I’m having to navigate,” he says.

If it’s someone Qureshi expects to deal with for a short period of time, such as at a conference, he looks for things such as jewellery or hairstyle – things that probably won’t change. “I have to expend mental effort memorising aspects,” he says. “Over longer periods of time, it’s more difficult.” Now he knows what face blindness is, he will tell people he has it, and if they have arranged to meet, he will ask them to approach him.

For some people with prosopagnosia, it may be a perception issue. “Because they’re seeing faces a little bit differently to everybody else, it doesn’t allow them to pick up on the visual cues that the rest of us use to distinguish between different people,” says John Towler, lecturer in psychology at Swansea University. They can have problems processing the whole face at a single glance, and will focus on a particular detail to remember people by – the eyebrows, or a mole or piercing for instance.

For other people with the condition, it may be more of a memory problem. “Obviously, if the perception is poor, then memory is going to be poor and the two things often correlate with each other,” says Towler. “But for some people, it’s primarily one or the other.”

Towler hasn’t been aware of more people reporting face blindness after Covid, though he’s open to the idea that it could be a symptom. “We know about the brain fog and the attentional problems associated with Covid. I think for some people, those areas of the brain that are responsible for face recognition become affected.”

Sarah O’Connell, 38, developed some face blindness with her myalgic encephalomyelitis (ME), also known as chronic fatigue syndrome, which was triggered by norovirus 10 years ago. “I noticed after a couple of years that it had become a bit of an issue,” says the former business analyst. “It was mostly with people I had only met a few times. At the school gate, people would say, ‘Hi, Sarah’ and I would be looking at them blankly. It took more exposure to someone’s face for me to remember it.”

She got Covid in summer 2021, then again in spring last year. “Since my second Covid infection, all my cognitive impairment issues got worse – memory issues, word-finding, losing my train of thought halfway through a sentence – and face blindness,” says O’Connell.

She recognises family and close friends, “but it can be quite embarrassing when people know you, and you have no recollection as to who they might be”. She gets around it, she says, with “just a generic ‘hello’. I play along, and hope I don’t get caught out.”

Although it’s too early to say whether prosopagnosia will become a recognised effect of Covid, Kieseler’s research, which was widely reported, has raised the profile of the condition, which many have welcomed. Angela Draper, a retired teacher, first read about prosopagnosia in an education journal when she was in her 50s. “I realised that described me. I was so relieved – almost tearful.”

The journal mentioned university research that needed participants, and Draper volunteered; when she was tested, she found out she had significant prosopagnosia. She realised that her father had also had it. “Both I and my father thought my mother was brilliant at recognising people and then I realised she was normal and we were the ones that were way out.”

On occasion, this has even meant not recognising herself. In a photo taken at her brother’s wedding, where she and the other bridesmaid were in identical dresses and their hair styled the same way, she says, “I can’t tell which is her and which is me.” Draper didn’t recognise her best friend, someone she had known for 15 years, because the friend was wearing a hat and a new coat. “If it’s friends or family who I’m not expecting to see, I don’t recognise them until they speak, or by the way they walk. And clothes.”

Teaching in a school was difficult, with children whose voices sounded similar, and who all wore identical uniform. She has learned to remember people’s wardrobes. “It’s a bit difficult if somebody has their hair restyled or changes the colour, or if they get new glasses. I try and memorise as much as I can about a person that isn’t changeable so I don’t get caught out. I play in orchestras and it’s easy because everyone sits in the same place and when they’re holding their instrument, you know who they are, so you get lots of clues like that. But if you’re at something like a party then it’s much harder.”

She has developed strategies, such as standing behind someone she thinks she might know and saying their name – if they turn around, she was right, if not, nobody is offended. “I just smile at people benignly [when walking past] because I might know them, or I might not.” When she is first talking to someone she may have met before, “you wait for more clues,” she says. Sometimes they turn out to be a total stranger.

Some people with prosopagnosia can find it extremely isolating, and can become socially anxious and avoidant, but while Draper is single and happily lives alone, she has a busy social life. She is upfront about the condition when she first meets someone. “I’ll say: ‘I’m sorry if I don’t recognise you next time we meet, but I can’t remember faces.’” Often the other person will say they’re terrible with names too, which Draper finds frustrating – she’s good with names, it’s faces that don’t stick. “It is amazing to people who aren’t prosopagnosic that it can be like that.”

For more information about prosopagnosia visit faceblind.org.uk