As daily washing became more in the modern era, the rise of chemical deodorants soon followed. Aerosol versions, led by Gillette’s Right Guard, became popular in the 1960s but eventually fell from favor because of health and issues. Many people have since turned back to natural deodorant crystals. Both potassium alum and ammonium alum crystals are highly in water. Applied under your arms, they quickly as you sweat, leaving behind a layer of salt that provides from odor-causing bacteria.

(Excerpt from 'The strange histories of the stuff we put in—and on—our bodies’, https://www.nationalgeographic.com, 2023)