Given that there are no proven biological markers for what is known as gender dysphoria, however, there is no consensus in the medical community on the central question: whether teenagers, habitually trying on new identities and not known for foresight, should be granted an irreversible physical fix for what is still considered a psychological condition.

The debates invoke biology, ideology and emotion. Is gender dysphoria governed by a miswiring of the brain or by genetic coding? How much does it stem from the pressure to fit into society’s boxes — pink and dolls for girls, blue and sports for boys? Has the Internet liberated teenagers like Kat from a narrow view of how they should live their life, or has it seduced them by offering them, for the first time, an answer to their self-searching, an answer they might later choose to reject?

Some experts argue that the earlier the decision is made, the more treacherous, because it is impossible to predict which children will grow up to be transgender and which will not.

“Basically you have clinics working by the seat of the pants, making these decisions, and depending on which clinic you go to, you get a different response,” said Dr. Jack Drescher, a New York City psychiatrist and psychoanalyst who helped develop the latest diagnostic criteria for gender dysphoria.

On the other hand, Dr. Drescher said, “Is it fair to make a child who’s never going to change wait till 16 or 18 to get treatment?”

A Teenager’s Pain

Kat Boone did not fit the stereotype of a girl trapped in a boy’s body.

As a child, she dressed in jeans and shirts, like all the other boys, and her best friend was a boy. She liked to play with cars and slash bad guys in the Legend of Zelda video games. She still shuns dresses, preferring skinny jeans and band T-shirts.