Alum has been used for many years, as a deodorant, astringent and basic antiperspirant. Alum is found in crystal deodorants, a type of alternative deodorant in the form of potassium alum.
Crystal deodorant is usually available as a stone, roll-on, or spray. Often built as the alternative to conventional deodorant, alum still contains aluminium, often hydrated potassium aluminium sulfate, (otherwise known as potassium alum). There is no scientific evidence that suggests alum is not safe.