What are Deodorant Stones?

Natural deodorant stones are made of potassium alum, a type of mineral salt and water.  The mineral salt is combined with water, formed into a ball or rock that resembles a crystal and dried.  This mineral salt "crystal" works by inhibiting growth of odor causing bacteria on the body. Potassium alum doesn't block perspiration, instead it prevents growth of odor causing bacteria.  

Note: For individuals with sensitive underarm skin, mineral salts can cause irritation.