Puberty can be an awkward time for anyone - but, for the Guevedoce children of the Dominican Republic, puberty is even more difficult.
Why? Because they literally appear to change gender when they hit adolescence.
As covered in the new BBC series, Countdown to Life: The Extraordinary Making of You, one in 90 children in the village of Salinas appear to be completely female at birth and are brought up to be little girls.
But, when they reach puberty, they develop penises.
“When they’re born, they look like girls with no testes and what appears to be a vagina"
So common is the transition that the children are referred to as Guevedoces, which translates roughly to “penis at 12 years”.
Writing for The Telegraph, Dr Michael Mosley explains: “When they’re born, they look like girls with no testes and what appears to be a vagina.
“It is only when they near puberty that the penis grows and testicles descend.”
He went on to explain that, despite the transition, the children usually adjust well to their new genders.
“Apart from being slightly undersized, everything works and the Guavadoces normally live out their lives as men,” he said, “albeit with wispy beards and small prostates.”
Johnny, 24, was brought up as a girl before he grew a fully-functioning penis at the age of seven.
He told Dr Michael Mosley: "I remember I used to wear a little red dress.
"I was born at home instead of in a hospital. They didn’t know what sex I was. I went to school and I used to wear my skirt. I never liked to dress as a girl."
Despite some initial teasing from classmates, Johnny - formerly known as Felicita - insisted that the change has ultimately been a positive one.
“When I changed I was happy with my life,” he said.
So what causes the unusual condition?
Well, babies usually form male sex organs after around eight weeks in the womb, with the change triggered by hormone dihydro-testosterone.
However a handful of babies do not have the enzyme that triggers the hormone surge and consequently appear to be born female.
This means that they do not form male genitalia until they reach puberty, when there is another surge of testosterone.
You can watch Countdown To Life: The Extraordinary Making Of You on BBC iPlayer now.