Student Mars Proppe, who identifies as nonbinary ¡ª neither male nor female ¡ª hoped one day to have a passport marked ¡°X¡± for gender. But when Iceland¡¯s government made that choice possible a year ago, Proppe had second thoughts.

While more than a dozen countries have introduced gender-neutral travel documents, some nonbinary and transgender people are reluctant to use them because they fear facing discrimination or bureaucratic hurdles when traveling abroad.

¡°I have yet to go and get my master¡¯s degree and hopefully travel through the world, and that¡¯s not something I think I can do ... if I have an ¡®X¡¯ on my passport. At least I can¡¯t do it really safely,¡± said Proppe, 23, who studies astrophysics.