Puberty can be an awkward time for anybody, but spare a thought for the Guevedoce children of the Dominican Republic, who literally appear to change their sex when they hit adolescence.
As covered by Michael Mosley in the 2015 BBC series, Countdown to Life: The Extraordinary Making of You, the remarkable case of the Guevedoces is a condition that affects just over 1 percent of the boys born in Salinas, a remote village lying in the southwest of the Dominican Republic.
Guevedoces (literal translation "penis at 12") - who are also called "machihembras", meaning "first a woman, then a man" - appear to be completely female at birth and are brought up to be little girls.
"When they're born, they look like girls with no testes and what appears to be a vagina," wrote Mosley for The Telegraph back in 2015. "It is only when they near puberty that the penis grows and testicles descend."
After the developments of puberty, Guevedoces grow up to be fully functional males in their society, although some telltale signs do give away their unique biological heritage.
"Apart from being slightly undersized, everything works and the Guavadoces normally live out their lives as men," wrote Mosley, "albeit with wispy beards and small prostates."
Not all Guevedoces in the Dominican Republic change their name upon hitting puberty – some grown men in the region have female names throughout their life. The condition is not isolated to just the Dominican Republic, it's also been observed in Turkey and New Guinea.
For his documentary, Mosley met Johnny, a Guevedoce male who was raised as a little girl, Felicita. When Felicita turned seven, puberty brought more than the usual changes that most people experience.
"I did not feel good, I no longer liked to wear a skirt, and I was no longer drawn to play with girls. All I wanted to do is play with toy guns and boys," Johnny said. Along with the psychological changes came physiological ones; Johnny grew testicles and a penis.
Despite being teased at school, the transformation was ultimately a positive. "I never liked to dress as a girl… When I changed I was happy with my life," Johnny said.
The discovery of why the Guevedoce children undergo their radical transformation was made decades ago by Julianne Imperato, an endocrinologist from Cornell University in the US, who travelled to the Dominican Republic in the 1970s.
Imperato and her colleagues found that a deficiency in the enzyme 5-α-reductase was responsible for the Guevedoce's rare condition.
Without this enzyme, the body doesn't create the male sex hormone dihydrotestosterone (DHT), which prevents the development of male sex organs – until puberty hits, at least, when increased levels of testosterone belatedly reveal that Guevedoces are, in effect, male.
Preceding puberty, however, "the postnatal external genitalia appear to be an ambiguous clitoris and labia," wrote Elizabeth Kelley for ISSUES Berkeley Medical Journal.
Strangely enough, Imperato's discovery was also the foundation of the medicine Finasteride, which is used by thousands, if not millions, of men worldwide to combat both prostate enlargement and male pattern baldness.
As for Johnny, the young man who used to be a young girl hopes to find true love one day, according to Mosley. Despite a number of short-term girlfriends since making his transition to masculinity, Johnny is still looking for the one.
"I'd like to get married and have children, a partner who will stand by me through good and bad," he said.
A version of this article was originally published in September 2015.