No single explanation Why are so many girls questioning their gender?

In 2009 the NHS's gender identity development service (Gids) saw fewer than 50 children a year. Since then demand has increased a hundredfold with more than 5,000 seeking help in 2021-22.

- Andrew Gregory, Tobi Thomas, Amelia Gentleman

In her review of gender services, Dr Hilary Cass said there had been a "dramatic increase" in presentations to gender clinics in a decade and, in particular, a rise in birth-registered females. In 2009, Gids treated 15 girls. By 2016, that figure had risen to 1,071. "There has been a significant change in the population of young people over the last 10 to 15 years," Cass told BBC Radio 4's Today programme yesterday. "So about 15 years ago, the service was seeing perhaps 50 predominantly births registered boys in childhood. And over the last 10 years or so it's switched to over 3,000 young people, and it's mainly birth-registered girls presenting in early teens... often with quite complex additional problems."

There is no single explanation for these rises, her review concluded. But it says various factors may explain the increase in predominantly birth-registered females presenting to gender services in early adolescence:

Social media and the internet Generation Z and Generation Alpha (those born since 2010) have grown up with "unprecedented" online access, the report says. This has huge advantages, but also risks. Greater access to the internet has given children and young people learning resources "but it has also made them vulnerable to new dangers", according to the review.

"Biology hasn't changed and adult biology hasn't changed in the last few years," Cass told the Guardian this week. "I don't think that young people today are being exposed to more abuse or trauma or so on than previous generations. We do have to think very seriously about the impact of social media."