Thread: Alum - Potassium vs Ammonium

I know potassium alum is recommended over ammonium alum for post shave skin treatment, but why?

When I tried one of the solid ammonium alum deodorant bars (Crystal) compared to my Bloc Osma bar the ammonium alum stung a bit where the potassium bar rarely does (unless I really screwed up my shave). I think the end result is the same but maybe with a bit more sting likely with ammonium alum.

One reason may be cost and coagulation power. Both are good astringents and absorb moisture. However, the potassium aluminum sulfate (Bloc Osma) and the even stronger burning aluminum sulfate (Styptic pencil) are well known as strong blood stoppers. I am not sure the the solid ammonium alum bar was meant to stop blood as well as perspiration?

The Ammonium simply isn't designed for your face. It's made for deodorant use. The potassium is more tame and that's why it's used on the facial prep. A styptic stick has an alum base but is different and is designed for bleeding.