In the past decade, the number of people who identify as transgender has grown significantly, especially among young Americans. Around 700,000 people under 25 identified as transgender in 2020, according to the Williams Institute, a research center at the University of California, Los Angeles, nearly double the estimate in 2017.

Gender clinics in Western Europe, Canada and the United States have reported that a majority of their adolescent patients were seeking to transition from female to male.

Because breasts are highly visible, they can make transitioning difficult and cause intense distress for these teenagers, fueling the demand for top surgeries. Small studies have shown that many transgender adolescents report significant discomfort related to their breasts, including difficulty showering, sleeping and dating. As the population of these adolescents has grown, top surgery has been offered at younger ages.

Another notable change: More nonbinary teenagers are seeking top surgeries, said Dr. Angela Goepferd, the medical director of the Gender Health Program at the Children’s Minnesota hospital, who is nonbinary. (The program does not perform operations but refers patients to independent surgeons.) These adolescents may want flatter chests but not other masculine features brought on by testosterone, like a deeper voice or facial hair.

After many months of deliberations over its new guidelines, the World Professional Association for Transgender Health initially decided to endorse top surgeries for adolescents 15 and up, part of a suite of changes that would have made gender treatments available to children at younger ages. But the organization backtracked this month, after some major medical groups it had hoped would support the new guidelines bristled at the new age minimums, according to Dr. Marci Bowers, a gynecologic and reconstructive surgeon and the president of WPATH, who is transgender.

“We needed consensus,” Dr. Bowers said. “I just think we need more strength for our argument and a better political climate, frankly, in order to propose this at a younger age.”