Victims of FGM are only offered surgery to reduce their pain. But a cult is supporting a few surgeons as they attempt to restore sexual sensation. Joanna Walters reports on the controversial procedure

A nondescript suburb on the outskirts of San Francisco. A plain brick building. Seven nervous women wait in the sunlight. They are here for surgery, which perhaps has as much claim as any other to describe itself as "miraculous".

The little building doesn't shout its purpose, for many reasons. First, this surgery is about female sexuality. Secondly, it is contrary to the beliefs and traditions of millions of families worldwide – brutal beliefs and traditions. And then there's the delightful surreality of the pair behind the procedure: the tall, blonde female surgeon – one of the best in the US – who happens to have been born male, and the cheerful French counsellor who follows the bizarre 1970s Raëlian sect that believes humans were created by extra-terrestrials for the purpose of unalloyed joy.

Soon afterwards one of the first patients, Zaria, 24, is under anaesthetic. "This one's pretty bad," says the surgeon, glancing at me from the stool where she sits between the legs of her patients, scalpel poised.

When I'd met Zaria, just before her operation, I was struck by the energy of this funny, feisty, beautiful young medical student with a tattoo and bundles of raven hair. Now, by her invitation, I am looking at her genitals over the surgeon's shoulder and trying not to cry.

Zaria looks more like a doll than a real woman. Her genitals are featureless, completely smooth apart from the opening. Barbie might actually be more anatomically correct.

Dr Marci Bowers in between surgeries. Photograph: Naomi Harris for the Observer

The surgeon lifts her scalpel and begins carefully slicing away at the flat skin surface; basically a thick layer of scar tissue. It is the second time in Zaria's life that someone has taken a knife to her most intimate parts. The first was when she was 11 in Sierra Leone, and that time there was no anaesthetic.

Relatives had taken her into the countryside under the ruse of a day-trip to pick oranges. Once there she was lined up with 20 other girls and forced to the ground by a cluster of older women. Her labia and clitoris were sliced off in a ritual once called female circumcision but now known more accurately as Female Genital Mutilation, or FGM.

"I remember I struggled and I was yelling so loudly that one of the women actually sat on my head and practically suffocated me while they cut me," Zaria told her fellow FGM victims as they swapped stories before their operations.

According to the World Health Organisation more than 140 million women worldwide live with the effects of FGM, which is most commonly practised in northeast and west Africa, but also in places such as Yemen and Indonesia. But an infinitesimal fraction, almost exclusively those who emigrated to the west, are now finding their way to an emerging handful of surgeons who offer a radical attempt at rehabilitation.

This surgery doesn't just make intercourse and childbirth easier. Controversially, it also aims to give the women the capacity to feel sexual pleasure – most for the very first time – by rehabilitating the clitoris.

Zaria has travelled to California from her home on the east coast of America, where she moved from west Africa as a teenager. The wounds from Zaria's cuts healed long ago, but in the process have formed a layer of thick scar tissue that has left her genitals numb to the touch.

"My fiancé left me two months ago because I don't want sex," she'd told me when she first arrived at the clinic, her sad and bewildered tone mixed with a note of defiance. "I did start having sex with him, but I don't feel anything and I don't care for it. He's from Sierra Leone, too, so he understands about FGM and was supportive at first, but in the end he went off with another African girl who hadn't gone through it and wasn't inhibited like me," she had said.

While some of Zaria's relatives dealt with her heartbreak by telling her she should just "get on with it" and have sex out of obedience, Zaria had what she describes as a "lightbulb moment" and began searching the internet.

In just seconds she had come across an alternative solution. Next thing, she had taken out a loan, which she has "no idea" how she'll pay back, jumped on a plane and found herself in this plain brick building.

Once at the clinic, she and the other patients (including one who had flown from Australia, who had been "cut" when living in Kenya as a young girl and who had hugged Zaria as she first told her story) were greeted by the two women who were instrumental in encouraging them to break their bonds of cultural taboo. They are an intriguing pair.

One is the surgeon, Dr Marci Bowers, who normally specialises in sex-change surgery, and indeed herself was born male before she transitioned. There's a 14-month waiting list for her $21,000 gender reassignment surgery, but twice a year she clears her diary to operate pro bono on FGM victims – although they must pay a $1,700 fee to the clinic, near San Francisco airport, where Bowers rents an operating theatre. So far she's operated on 50 such women.

The other is Nadine Gary, a Frenchwoman who lives in Las Vegas. A schoolteacher, she was inspired to help FGM victims by her following of the outré Raëlian sect. Founded by Claude Vorilhon ("Raël"), who spouts absurd claims about being taken up in an alien spaceship to meet Moses, Jesus and Buddha, it professes that humans – and all living things on Earth – were created by extra terrestrials using genetic engineering. Followers strive to campaign for world peace, sharing and nonviolence, but also unfettered sexual joy, which is what drives their movement against FGM. They were most recently in the news for offending people with their use of the swastika, often set inside the Star of David.

When I meet her, Gary is wearing this scandalous combination on a gold necklace and, noting my alarm, explains at length why it symbolises infinity for Raëlians and employs the swastika in the ancient eastern sense of sacred goodness "before Hitler hijacked it". I waver between dismay and bemusement.

She comes across as a paradox: an unambiguously dynamic, charming, kind and generous person in all our conversations who, until she starts talking about UFOs, seems rational. I deal with the discomfort by listening politely, but then turning back to the practical and political implications of the charity she helps run, provocatively called Clitoraid. Formed by the Raëlians, it campaigns for the end of FGM and, meanwhile, promotes the surgery to victims and offers free long-term emotional and sexual counselling.

Gary has driven across from Vegas to support the women, many of whom have not told their families about their journey. The atmosphere in the clinic is more than a little surreal. There is much nervous laughter.

On the operating table, however, everything is clinically methodical. After stripping off old scar tissue, Bowers makes deeper incisions to disconnect small ligaments around the area where Zaria's clitoris was before it was removed. At the stroke of the scalpel, a prominent nub of raw pink flesh practically pops up, suddenly protruding from the tissue surrounding it.

"There! That's her womanhood right there," Bowers declares triumphantly. She pauses for effect. "It's like a magnificent tower in the forest." What's barely understood, Bowers explains, is that when the clitoris is cut off in FGM, it's like losing just the visible "tip of the iceberg".

"The clitoris is much larger than previously advertised. Even after they cut off the tip, about 99% of the clitoris is actually still intact, but hidden beneath the surface. We can access that." Apparently women possess another eight inches of unseen clitoral erectile tissue that lies under the skin, arching around the vagina. "Two inches longer than the average penis," says Bowers, archly.

By removing the obstructive and often painful scarring and exposing some of that remaining erectile tissue, then stitching it finely into place, she asserts that after about two months of healing it can function as a new clitoris, restoring the potential for pleasurable sex.

After that procedure, known as clitoroplasty, Bowers then stitches some side folds of spare skin near the vagina to give Zaria the token appearance of labia minora. It can never be her natural perfection, Bowers warns. But even to my non-medical eye, I can see that this travesty, this sub-Barbie, has been transformed into a fair simulacrum of what Zaria had been born with. And, luckily, she has not suffered the infibulation ritual that stitches the vagina partially shut.

After 55 minutes she is wheeled out of surgery and the next patient, Sara, 29, is wheeled in. Sara was cut in Eritrea, East Africa, at the age of just three months and it was more a symbolic slash than a mutilation. But the manner in which her scar tissue formed fused a section of the labia, restricting the vagina and clitoris. Now living on the west coast of America, Sara suffers pain, not only if her boyfriend attempts to touch her there, but even when doing exercise, such as yoga. In just 12 minutes of delicate scalpel work, Bowers removes a lifetime of discomfort for Sara.

Between sessions, Bowers checks her emails, gulps a coffee and chats with the nurses in an ante room. She's exasperated that more surgeons aren't training and research hospitals aren't adopting this operation, describing progress in the field as "glacial".

Compared with the delicate gynaecological, urological and plastic surgery she uses for five-hour gender-reassignment operations, FGM-restorations are a doddle.

"Clitoroplasty isn't rocket science. If I wanted to be controversial I'd say that the three reasons why more surgeons don't train for it are that these patients are African, Islamic and female. There's a cultural bias or indifference there, combined with good old racism and sexism in a traditionally paternalistic medical profession.

"There may be some legitimate fear about interfering with other people's cultures, but when you talk to the husbands and boyfriends of the women they're not happy that their wives and girlfriends cannot respond sexually – and that's even without going into the misery that the women suffer," says Bowers.

There is, as you might imagine, disagreement in the medical world about the effectiveness of the surgery. The pioneer of FGM repair surgery is Dr Pierre Foldès in Paris, who began offering the clitoroplasty two decades ago and has operated on almost 3,000 women. He has trained Bowers, 10 more surgeons in France and one in Barcelona, and another doctor who has started offering the surgery in upstate New York. (The reason, incidentally, why there are so many French trainees is that clitoroplasty is paid for by the state as corrective surgery, not only to increase the chance of sexual pleasure, or at least reduce the chance of sexual pain but, crucially, to make women feel normal again; the French see this as a human right.) Just one surgeon in Britain, Dr Kamal Iskander, based at Northwick Park Hospital in Middlesex, is known to perform the occasional clitoroplasty on a patient but, he explains, only if he's already operating on them for more extensive post-FGM problems, such as chronic pain or infibulation.

There are an estimated quarter of a million women in the US who have suffered FGM or are at risk of it. In Britain there are an estimated 66,000 victims, largely among the African diaspora, and a further 20,000 of their children are believed to be at risk, mostly of being taken abroad for the ritual, even though this is illegal.

An article in the Lancet by Foldès in June last year stated that of those who attended a one-year surgical follow-up consultation (admittedly only 29% of his patients), more than half were now having orgasms and almost 98% felt clitoral pleasure. But leading British doctors Sarah Creighton, consultant gynaecologist at the private Portland Hospital, Susan Bewley, consultant obstetrician at St Thomas's and Lih-Mei Liao, clinical psychologist in women's health at University College Hospital then wrote to the journal countering that his clitoral restoration claims were "anatomically impossible".

Their letter went on to say that his results were not "supported by current evidence" and "where the body of the clitoris has been removed, the neurovascular bundle cannot be preserved". Outraged, Bowers described the letter as "sneering", citing patients who ring her up crying with happiness after their first ever orgasm.

Efua Dorkenoo, who leads the campaign against FGM at the women's anti-violence pressure group Equality Now in London, called on the World Health Organisation to initiate clinical trials on the surgery urgently. She said there was such a lack of information, she could not dismiss either side's arguments.

Bowers tells FGM patients that "there are no guarantees" but that eight out of 10 report improvements in their sex life after her surgery, ranging from eliminating pain and acquiring some pleasure to full-on orgasm.

Gary organises a pre-surgery workshop about the mental transition needed from lingering trauma to embracing sensuality, and sends them all home with a vibrator. Once they've healed she sends them literature on discovering masturbation, and Gary and Bowers give all the patients their phone numbers and email. "The physical surgery is just one step of the journey. Many religions repress women's sexuality – we break the taboo. A woman's body is connected to her self esteem – we explain to the patients the many different things that happen when a woman feels pleasure, and that it's natural," Gary says.

Two patients relax by their hotel pool during their recovery period. Photograph: Naomi Harris for the Observer

Miriama, 30, who was born in Guinea but now lives in the US, had the surgery with Bowers three years ago and says it's changed her marriage. "Sex with my husband is fun now; it was just a duty before. I haven't reached the orgasm part yet, but I'm working on it."

Travelling to Bowers's clinic had been a huge step. "When I told a cousin what I was getting done she called me a slut," Miriama recalls.

She has a daughter, who is eight, but Miriama refuses to take her to visit her mother, who still lives in Africa and has never met her granddaughter, in case the child is snatched and taken to be cut, as Miriama's mother did to her.

Natasha, 35, who also moved to the US from Guinea, had the first orgasm of her life three months after her 2010 surgery with Bowers, using the vibrator Gary gave her. "I'd never felt anything like it before; these waves of excitement came over me and I lost control – it's very intense, quite amazing."

She now has regular orgasms and in case doubters think they're imagined in a misplaced eagerness to be convinced that the surgery worked, she points out that she climaxes in her restored clitoris despite what's in her head, not because of it – "I was surprised that I actually felt a little bit ashamed, I felt guilty that I was doing something selfish and dirty."

The social conditioning of her upbringing is hard to shake. Her husband is making efforts to reassure her, she said, and she also turns to Gary for support. "I can talk to Nadine freely. She feels like a big sister." Natasha and the other women say that Gary talks of the Raëlian philosophy of sexual freedom, but absolutely deny that the treatment has been used as an attempt to convert them to the outlandish religion.

When I question Gary further on her beliefs, she explains that the aliens who created humans are called "Elohim", which is generally taken as Hebrew for god or gods but which, to the Raëlians, means "those who came from the sky".

"The Bible is essentially an atheist book," she tells me earnestly. "There is no God." Gary says this set of beliefs seemed more "mature" to her when she converted at 17 from the Catholicism that surrounded her when growing up near Lyon. She is now, she adds, a Raëlian priestess.

I turn to Bowers, who shrugs. "The Raëlians are very unabashed about their sexuality and unapologetic about erotic pleasure, but it's a red herring in terms of my work. It doesn't affect the price of bread," she says.

"But they do deserve credit for promoting women's sexual health and Nadine has got me talking much more frankly about sexual matters with my patients."

Bowers was supposed to be travelling to the small west African state of Burkina Faso in October to celebrate Clitoraid opening a hospital there. When it happens, it will be Africa's first clinic specifically for performing FGM-restoration surgery, including clitoroplasty – a highly symbolic act at the heart of a region where the ritual is prevalent.

Clitoraid says local medical staff and surgeons will be trained to work there and that several hundred local women have already broken the taboo to sign up for operations. Critical voices have accused Clitoraid of neocolonialism, and of using the hospital as a fundraising tool. Gary fires back that their motive is purely humanitarianism. Yet the opening, which has been delayed several times, has just been put back to next year.

Campaigners hope FGM will be phased out within a generation, to join Chinese foot-binding as a horror of history. "The idea of reducing women's sexual pleasure with FGM so they can be controlled is falling apart because men are having sex outside their communities and seeing the difference, and it's creating problems within relationships, here but also in Africa," says Efua Dorkenoo, of Equality Now.

Facing the future: 'Zaria' awaits surgery while 'Sara' recovers. Photograph: Naomi Harris for the Observer

The day after her surgery in San Mateo, Sara is tired but ecstatic. Most of the women are dotted around in various cheap hotels near the clinic, recovering, but Sara is collected by her boyfriend, who lives nearby. "I feel free. I'd felt so unheard and my whole life had felt like there was something missing. Now the anger I've had for years has gone," she says.

Her boyfriend Jack, who was born in Eritrea, puts up with the fact that they've been together for three years but don't have sex. "I'm not going to rush. I love her and she is my good match," he says in a soft accent, smiling shyly. "I'm very glad she got the surgery – for her. It's necessary for her to feel like a full woman."

Another of the women Bowers has just operated on, Ayanna, 23, a marketing assistant from the Pacific northwest who fled the civil war in Somalia, is in a quandary after her clitoroplasty, for she is not in love with her current boyfriend.

"I told him I was coming for the surgery and the way he was talking I'm worried he's going to expect me to be an instant sex machine," she says.

Ayanna lied to her conservative mother that she was visiting friends in San Francisco, then sneaked off to Bowers's clinic with her best friend Emma for support. Emma's parents are from Ethiopia, but she was born in America and was never cut. The two exude such an all-American youthful mischief it's hard to believe Ayanna was once steeped in a very different tradition. They banter about boozy parties and dating. They order room service while giggling in their dressing gowns. Ayanna shows off the scrapes on her leg from a skateboarding escapade the previous week.

But then she is suddenly solemn.

"My friends and I will all be in a nightclub having a crazy time, but while they are getting guys' numbers, I hang back," she says. "Technically there's no reason why, just because I'm cut down there, I couldn't feel sexy when a guy is kissing me or touching my breasts. But my mind leaps to what that leads to next and then I shut down," she says.

She has high hopes of a fulfilling sex life now that she's had surgery, but still has years of negative mind games to overcome.

Zaria feels the same and is not in a hurry to find a new man. She turns her eyes to the endless blue sky and lets the sun warm her between takes for the Observer's photo- grapher, 24 hours after the surgery.

Chattering nonstop, she's on a mental roller coaster – wanting to be the "face of Clitoraid" one minute, worrying about repercussions from her family the next. Excited about the notion of erotic pleasure, and equally scared. Weeping, laughing.

She finally pauses for breath. "I didn't do this to get back at my ex-fiancé, or get him back. This isn't about him or my family any more. It's all about me," she says.

Some names have been changed