Or make it so we sweat sunscreen when we eat the mayonnaise (on fries?).

Mayonnaise on fries is British. It's probably related but we'd have to market it differently.

(I've noted that the covers on the Harry Potter books in Britain seem to be drawn for intelligent people, whereas the books in the US are far more cartoony.)

There's an offshoot idea actually. Could you make a pill or food that turns you sweat and or skin oil into natural sunscreen?