Barry Wainwright. Photograph: Fabio de Paola

If I look at a photograph of myself, I don't know it's me. I don't recognise my wife or seven children, either, even when I'm looking right at them. I have the condition prosopagnosia, which can be inherited or caused by a brain injury, although neither applies to me. Its common name is face-blindness, but that term irritates me because it sounds as if I can't put a name to a face, which is something lots of people experience. This is different. True face-blindness is caused by an impairment in the right hemisphere of the brain that specifically identifies faces.

For me, the world is a sea of unfamiliar faces. If you suddenly developed prosopagnosia, it would be very frightening, but I've always had it, so it's all I've known. I can make out facial features perfectly well, but somehow they just don't connect with that person in my brain. When I walk down the street, as far as I know everyone I pass is a stranger. But when an old woman stops me and starts chatting, it's clear she must know me. So, while we're making small talk, I'm desperately searching the conversation for clues, to narrow down who she could be. It seems rude to interrupt and say, "Sorry, do I know you?"

I've had 54 years to hone my detective skills. Now they're pretty sharp. Generally, it's easier to recognise men because they're more likely to wear the same shoes. I have a mental Rolodex file: Steve = brown brogues. I also call people "love" or "mate" to avoid getting their name wrong, but sometimes my coping strategies fail and I start chatting to a stranger, thinking I must know them. Once I was talking to a friend, turned away to pick up my drink, then continued the conversation. The only trouble was I hadn't noticed he'd walked off and been replaced by someone else.

It's slightly easier with my family. I can identify my children through the way they walk and their mannerisms, and I always take note of what they're wearing, to keep track of who's who. One source of sadness is that I couldn't appreciate their school plays because I found it impossible to identify them on stage.

Voices don't really help; I find it easier to pinpoint a person through context. If someone comes downstairs in the morning, I know it must be my wife, Margaret. But if we go to the supermarket and I lose sight of her, I won't be able to find her. I walk up and down the aisles studying people's shoes and clothes for visual clues, hoping she notices me and waves. Now she always wears her "supermarket jacket" - a red one that is quite distinctive. When we first met, Margaret would get upset that I didn't notice a new haircut, but I explained that it's not that I don't care, just that I can't register any difference.

Growing up with prosopagnosia was difficult. From my earliest memories, I can remember having difficulty recognising people. This tended to make me shy and withdrawn. I became bookish, unpopular at school and bullied. I couldn't make friends because uniforms made it impossible to remember anyone. I was lost in the playground. I took to truanting frequently and fell far behind in my work. My parents were worried about me and in my teens sent me to a psychiatrist, but he didn't know what was wrong.

People don't generally discuss how they recognise someone - it's something they take for granted. I muddled through my teens and 20s, blanking people at every turn, until I met my wife. She changed my life; she introduced me to her friends and I learned how to interact with people.

Working for an engineering company in the rail industry has been a blessing because a lot of people wear name badges. I also love the phone because people say who they are straight away. The internet is great, too, because every email has the name of the sender in black and white - no guesswork there.

I found out what was wrong with me only three years ago, listening to a programme in my car - they mentioned prosopagnosia. I'd never heard of it, but as they described my symptoms I shouted, "That's me!" Finally I could understand why I've had a lifetime of blanking people and causing offence. Tests at University College London confirmed it. It was a huge relief. There's no cure, but at least now I can put a name to my condition. I'm not stupid, lazy or shy after all. It is just the way my brain is wired.