Well, I used to. And I still do when I travel.
It’s not for good luck - I use it in place of deodorant. No, it’s not homeopathy and no I don’t smell bad (or at least no one has had the courage to tell me yet).
What I’m referring to is a Thai salt crystal - a stick of potassium alum. It’s the stuff you find in some “aluminum free” deodorants.
Your average roll on deodorant coats your armpits in a film that blocks your pores. It makes it harder to sweat. In the past, my body (powerful as it is) pushed forth and sweat anyway, often staining my clothes with whatever I applied near that surface.
The salt crystal coats the surface instead in an anti microbial material. It does not block sweat, but instead stops the growth of bacteria. It is not your body, but this bacteria that causes the smell.
If you stop the bacteria, you stop smelling. I still sweat these days, but I don’t smell that bad when I do.
Wetting a salt crystal and rubbing on your armpits is weird and I don’t prefer it to other things as a method of application. When I’m at home, I use a salt spray, comprised of essentially the same materials.
The rock lasts much longer but I’m okay buying a new spray bottle every few weeks.