Deodorant crystal is the naturally occurring compound Alum (Potassium or Ammonium), not to be confused with harmful processed aluminium (Aluminium Zirconium or Aluminium Chlorohydrate). Aluminium is a metal while Alum is a compound. Many of these processed aluminium molecules in conventional antiperspirants can be absorbed into the skin and bloodstream. Alum molecules create a barrier against odour causing bacteria and contain a large molecule which does not penetrate the surface of the skin.
Moisten the stick and apply it to underarms. Be sure to completely cover the area to be protected as it forms a protective barrier against odour causing bacteria. Do not apply to broken skin.