Bangkok in January: Mornings are hazy, evenings are muggy. The days in between are still and hot. I’ve come here to learn more about sex reassignment surgery, both within Thai culture and within a larger context of global commerce and medical tourism. The country is one of the world’s leading destinations for the procedure, a place where sex changes are not only easy to come by, but also relatively cheap.

For centuries, Thailand has embodied a relative openness in navigating categories of sexuality and gender. Walk down the street in Bangkok, and you’re likely to see people labeled as kathoey, or “ladyboys.” The nation has one of the largest transgender populations in the world, a fact many people — surgeons, therapists, transgender people — find difficult to explain. Maybe it’s the relatively open Buddhist culture, one surgeon speculated. Perhaps it’s out of financial necessity, others suggested, alluding to a high demand for kathoey sex workers. Whatever the varied reasons, Thailand’s reputation is the antithesis of Iran’s when it comes to sexual openness. In Iran, same-sex acts are considered criminal and punishable by execution, but sex reassignment surgery is legal. For these reasons some gay Iranians report feeling pressure to change gender identities.

Over the past several decades, the world’s sex change “capital” has bounced between continents, from Africa and Asia to North America. In the late 1950s and 1960s, Morocco was home to one of the only physicians performing surgeries at the time, French surgeon Georges Burou, who treated patients with the technique he invented for male-to-female surgeries, an early form of a procedure known today as penile inversion.

Because of the growing private practice of surgeon Stanley Biber, Trinidad, Colorado, became known as the new capital through the 1970s and ’80s when Biber performed thousands of surgeries at the town’s small hospital for people from all over the world. Meanwhile in Bangkok, Thailand, Preecha Tiewtranon began performing procedures in the 1970s as well, building a private practice that soon gained an international reputation. As Thailand evolved into an international hub for medical tourism, the number of patients coming specifically for sex reassignment surgery — and the number of both trained and untrained doctors offering the service — also increased.

One afternoon in Bangkok, I take a motorcycle taxi to the sleek, very air-conditioned Preecha Aesthetic Institute, one of the country’s leading clinics for sex reassignment surgery. The first thing I notice when I meet with Prayuth Chokrungvaranont, a surgeon and faculty member at Chulalongkorn University, is a photocopied newspaper article, enlarged and framed, hanging on the office wall; “The Ayatollah and the Transsexual,” reads the 2004 headline from the Independent.

The Independent article reflects the celebratory take on sex change law in Iran and hangs on the wall because the Preecha Aesthetic Institute is one of Bangkok’s leading clinics for Iranians. Between 2008 and 2011, the clinic performed 108 sex change operations on Iranian patients, both male-to-female and female-to-male. Many patients who can afford to leave Iran for surgery come to Thailand in search of better standards of care.

“It’s really interesting that an Islamic country allows their people to change their sex,” Chokrungvaranont says, adding that he finds it “remarkable” that the clinic performs so many male-to-female surgeries when life as a woman is considerably more difficult within Iranian society. “Maybe she’s the reason,” Chokrungvaranont says, pointing to Maryam Hatoon Molkara, the transgender woman in the newspaper photograph who lobbied for the Ayatollah Khomeini to legalize sex changes. Sex changes were formally legalized in 1985, when the Ayatollah Khomeini’s 1967 fatwa sanctioning sex changes was reissued.

Earlier that day, the clinic’s staff saw a female patient from Iran who, several weeks from now, will return to her country one step closer to becoming male. The procedure for female-to-male surgery is far more complicated — and rare — than male-to-female surgery, requiring several surgeries rather than just one.

Chokrungvaranont considers “gender identity disorder” a medical condition, something that must be treated to decrease patient suffering (the American Psychological Association recently stopped using the term “disorder” in such cases to avoid pathologizing less common expressions of gender.) He describes surgery as medical magic. “We know that gender is what you feel, sex is what you see. To be happy these two should be harmonious,” Chokrungvaranont says, paraphrasing German-born endocrinologist and early advocate of sex change surgery, Harry Benjamin. The process of bringing that harmony is a long one, and often very challenging. “First you need to adjust the patient’s mind,” Chokrungvaranont describes, emphasizing the importance of hormone therapy and counseling. “Some patients are satisfied after they get hormones, breasts, and different skin texture, voice and hair. That’s enough, if the patient feels freed. But if the psychiatrist says it’s not enough and the patient is still suffering, then they come to us to change their sex.”

In 2009, new legal restrictions in Thailand began to require two psychological evaluations and a one-year waiting period for patients wishing to undergo sex reassignment surgery. Though Thailand is not the first country to require a waiting period or approval from licensed psychologists, the change is significant because Bangkok — due to the sheer number of people traveling to the city each year to undergo the procedure — is a place that exerts enormous influence in defining and shaping transgender identity worldwide. Bangkok, in adopting the new regulations, is catching up with other countries that already follow guidelines issued by the World Professional Association for Transgender Health. If Thailand wants to be an internationally renowned hub for sex change surgery, it is under considerable pressure to embrace internationally accepted standards.

“If we do everything that people want without any regulation or control, we will be in trouble. People won’t trust us,” says Somsak Lolekha, former president of the Thai Medical Council, the doctor who was in charge when the stricter 2009 regulations were passed. As Lolekha describes, the regulations were put in place for a multitude of reasons: to try to guard against underage castrations; to make sure people (foreigners and Thai both) are getting sex reassignment procedures they won’t later regret; and to help ensure that Thailand has a reputation in the international realm that is responsible and not of a lawless, wild west of medical tourism. “I don’t think [transgender identity] is understood well enough,” he says.

I meet Nada Chaiyajit, 33, who had male-to-female surgery performed by a surgeon from the Preecha Aesthetic Institute in 2008, on a Saturday morning for coffee at a busy shopping mall in Bangkok. Youthful and studious looking in glasses and a cardigan, she tells me about her various lives as a man, woman and activist. An advocate for transgender people, even Chaiyajit was unprepared for waking up in her new body. “My head was blank,” she says, describing a feeling of immense emptiness. “There was nothing in my head. I didn’t know how to control my pain — not just physically, but also in my heart.” One of her biggest fears following the operation was that part of her soul might have been removed. “I felt like there might be something wrong in the future because I cut it,” she says, adding that she grew up in a religious household, raised Muslim. “The body is a basement for the soul.”

Today, Chaiyajit identifies as a transwoman — something “beyond a woman,” she says — and does her part to help people like her former self. She has mentored thirty transgender patients through the surgery process — helping them with everything from the basics, such as how to feed, clean and dilate themselves after surgery, to more complicated tasks, such as how to adjust mentally and emotionally to life in a new body.

“Who sets the norm?” Chaiyajit asks, articulating one of the most profound and persistent questions of gender and sexuality. “Why do we have to suffer?” Four years after her surgery, she has found peace with how her body and soul seem to be fitting together. Life after surgery isn’t perfect, she says, but is better than life trapped in the wrong body. “The problem was like a bomb just waiting to explode.”