Perhaps I have no business posting on this forum but there is a terrific product for divers and snorkelers called "Seasafe". It is a sunscreen available in different SPFs that actually protects against jellyfish stings. It works! Not sure if it works with every species, but it seems to have been well researched and it has been on the market for awhile. I am of Scotch-Irish descent so I need to use sunscreen anyway. Even in a full wetsuit I put this stuff on my ears and face (I don't wear a hood) and any other exposed skin (hands, ankles). I have never been stung, knock wood, even when there were tiny stingers in the water and everyone else was getting a jellyfish 'rash'.
You won't likely find it in cosmetic shops but many dive shops carry it.
I am not associated with the company that makes this, just trying to be helpful.
Thomjinx