Adam Pearson is used to people noticing him. A few weeks ago, he was in a DVD shop near his home in Croydon, south London, and a gaggle of teenage girls starting talking loudly about him and taking photos of his face on their smartphones. "They were saying 'Oh, look at that man'," says Pearson. "And all I wanted to do was buy The Hobbit on Blu-Ray."

Pearson suffers from neurofibromatosis, a condition that affects one in every 2,300 people and which causes non-cancerous tumours to grow on nerve tissue. In his case, the majority of these tumours are on his face although, he adds drily, "I've got one on my arse I probably won't show you". Throughout his 29 years, he has been bullied, harassed and called everything from Elephant Man to Scarface.

Every time he goes out, people stare. On the way to our interview, Pearson was stopped by a couple of passersby as he got on the train. This time, however, it was not as a result of his condition – it was because he has begun to be recognised. Pearson is currently starring alongside Scarlett Johansson in Under the Skin, a critically acclaimed science fiction film directed by Jonathan Glazer about an alien who roams the streets of Glasgow abducting and killing unsuspecting men. In one of the most poignant scenes, the alien (Johansson) is shown picking up a hooded man at night (Pearson). When the unnamed man reveals his disfigured face, it is a pivotal moment: the alien becomes humanised and conflicted. The two of them have a brief conversation about the nature of ignorance and prejudice. The alien does not remark on the stranger's face, instead complimenting him on his "beautiful" hands.

"One of the main reasons for taking the role was because it was so moving and honest," says Pearson over a lunch of fish and chips in a south London cafe. "For me, the film is about what the world looks like without knowledge and without prejudice. It's about seeing the world through alien eyes, I guess."

Much of the dialogue was improvised. Pearson and Johansson had a conversation beforehand about where it might go – the line about the hands, for instance, came from him. "My mother likes my hands," he says now, a touch embarrassed. He also had to film a nude scene with Johansson – something even the most experienced actor would be nervous about.

"They just said 'action' and you do it," he says. "I didn't really think about it ... I didn't broadcast the information [that he was in the film] until quite near the release. I didn't tell some people at all and just took them to see the film. I mean, my friend Heidi hasn't made eye contact with me for a week."

Johansson was "brilliant. She's really nice, charming, funny and intelligent once you get over the feeling of 'Oh my God, this is Scarlett Johansson!'"

One of his favourite memories was engaging the actress in a two-way competition to see who could tell the most inappropriate joke. Pearson won, but Johansson put up an excellent fight (and the jokes in question are eye-wateringly unrepeatable).

More importantly, Under the Skin gave Pearson an opportunity to challenge what he sees as the stigma surrounding representations of disfigurement on screen. "There's a lot of fear around the unknown. If I can try to be as normal as possible and show there's nothing to fear – either on film or day to day, going round the corner to go shopping for milk – then the more people see it in wider society, the less stigma there is. If I just sit at home and mope, hugging the dog and crying, nothing's going to change."

He points out that facial imperfections are often used as shorthand for evil in films, whether it be Blofeld's eye scar in James Bond or the villain in Disney's recent adaptation of The Lone Ranger, whose face was severely scarred and who was given what appeared to be a cleft palate in makeup. "It's always used very lazily," explains Pearson. "In an ideal world, actors with conditions would play the characters with these same conditions, but that's a way off. Instead, film-makers tend to get a generic, 'normal' actor and use prosthetics. If they'd got Adam Sandler and blacked him up to play Nelson Mandela, there would have been an uproar ... but with scars and stuff, it seems like people are cool with that."

In person, Pearson is both eloquent and extremely funny. He possesses a quiet confidence and a degree of self-awareness that is rare among young men in their 20s. As a child, he had to grow up fairly quickly. He was diagnosed with neurofibromatosis when he was five, after he knocked his head on a windowsill and the resulting bump refused to go away.

His identical twin, Neil, was also diagnosed with the condition, but in him it takes a different form. "He looks normal," says Pearson, "but he's got terrible short-term memory."

Secondary school in Croydon was tough. He was insulted and bullied on a regular basis and no one knew what to do about it. He remembers one occasion when a so-called friend said a teacher wanted to see him in one of the classrooms. When he got there, Pearson was assailed by a group of his peers who had been lying in wait. "I went home with spit all over my blazer," he says. "That was horrific."

Throughout all this, Pearson was having operations to "debunk" some of the tumours; to date, he has undergone 30 medical procedures. As a result, he is understandably sceptical about the rising trend in elective cosmetic surgery. "I'm not a fan of cosmetic surgery profiting from people's insecurities," he says. "I read somewhere nine out of 10 women don't like how they look and I think that's because they're comparing themselves to the airbrushed images they see in Vogue or FHM. People lack a real literacy in the media. They don't know what goes into producing these images. Media literacy should be part of education. I think we've done beauty a great disservice by quantifying it."

It was during one of Pearson's regular visits to Great Ormond Street hospital for treatment that he saw a poster advertising the organisation Changing Faces, which helps people and families who are living with conditions, marks or scars that affect their appearance. Pearson got in touch and asked for help without telling his parents – the first they knew about it was when the literature arrived in the post. The charity gave him coping mechanisms, encouraging Pearson to keep positive and to remember that "they [the bullies] are the ones with the problem, not you".

Things got better when he went to Brighton University to study business management. After graduating, he had jobs in television production for the BBC and Channel 4, where he is still involved in casting for series such as The Undateables and Beauty and the Beast, both of which challenge society's notions of disability.

It was while he was at Channel 4 in 2011 that he got an email from Changing Faces saying that a film company was looking for a male character for Under the Skin. Pearson replied and got the job. The film has been an overwhelmingly positive experience, and not just because he left with Scarlett Johansson's personal email address.

Pearson is keen to do more acting. He'd like to get a girlfriend ("I'm currently single") and, although there's a 50% chance he could pass his condition on to any children, this doesn't worry him unduly: "My kids will be genetically awesome anyway."

At the moment, he is living with his retired parents, Marilyn and Patrick. Are they proud of his recent achievements?

"It's certainly a good topic of conversation between them and their friends," he says. "A friend will say: 'Our daughter just got into Cambridge' and they'll go: 'Adam's in a film with Scarlett Johansson.'" He polishes off the last of his battered cod. Then he adds: "Booyah! Competition over."