Tami Staas, 51, a schoolteacher who lives in Tempe, Ariz., and is president of the Arizona Trans Youth and Parent Organization, has a 21-year-old son who was assigned female at birth and who started binding at 12. He wore a binder about 12 hours a day for five years. He had trouble in gym class and breathing trouble.

“It was like trying to run a marathon in a tight bustier,” Ms. Staas said. “It was difficult for me to weigh: Am I doing the right thing? Is it causing irreparable damage? It was very difficult to watch him cause himself physical pain in order to be comfortable in his own skin.” At 18, he had a double mastectomy, or top surgery, and now takes testosterone weekly.

A 17-year-old in Phoenix who binds daily and asked to be identified only by the initials J.M. said he started binding at 13. To maximize the compression, he bought a binder one size too small and wore it at night. “My arms and hands would feel numb and tingly off and on,” he emailed, “from how tight the material was around that area.” When he removed the binder, he found his skin “severely chafed and raw.”

He added: “The divots left behind from those times took months to heal. In all honesty, I couldn’t have cared less about the damage being created, just that my chest was flat.”

Dr. Ilana Sherer, a pediatrician and founder of the Child and Adolescent Gender Center at the University of California, San Francisco, Benioff Children’s Hospital, emailed that “binders can be physically very uncomfortable and can cause problems especially if overused or ill-fitting, so it’s important that every youth weigh the risks and benefits for themselves and have access to quality, well-fitting binders.”

But even those are correlated with negative health effects. Though there have been no studies on binding and adolescent health, because of ethical concerns about research on minors, a 2017 study by students at the Johns Hopkins Bloomberg School of Public Health, the Boston University School of Medicine, and the Boston University School of Public Health looked at 1,800 transmasculine adults with a median age of 23. Seventy-eight percent of respondents said they had bound for over a year, over half bound an average of seven days a week, and 66.6 percent were interested in top surgery. An additional 13.1 percent had already had the surgery.

Participants reported a statistically significant improvement in mood after binding. They also reported decreased gender dysphoria, anxiety and depression. As for physical effects, 97.2 percent of the group that bound reported at least one negative physical symptom, such as back pain, overheating, chest pain and shortness of breath. Other symptoms included numbness, bad posture and lightheadedness.