How do you change gender on Poptropica?

Because the Poptropica characters, and the story characters, can have any number of costumes (especially on Nabooti island*), there is one characteristic that can determine the gender of a character. That is the lips. Female interactive characters have the "pursed" or colored lips, wider in the middle.

The only way for a male character to get these lips (so far) was the Blue Fairy outfit from the Tinkerbell ad game, which strangely allowed parts of the female costume to be worn by males (necessary because the Pixie Dust reward was for both genders).

* Female users whose characters adopt scanty outfits will discover that the girls are uniformly wearing a "sports bra" under their tops.