Aluminum has long been known to have neurotoxic effects in humans and other animals. Most aluminum used in deodorants and antiperspirants exists in either aluminum salts or aluminum-glycine complexes. These vary in their chemistry and ability to cross the skin. Aluminum chloride has been shown to have health impacts on monkeys, mice and dogs. The aluminum-zirconium trichloro- and tetrachlorohydrex glycine complexes that are currently being used more widely in deodorants, however, are bigger molecules that work to plug up the sweat glands and do not as readily cross the skin barrier. However, researchers continue to disagree about the risk of aluminum use in deodorants and antiperspirants, particularly the correlation of aluminum and other compounds and cancer in the upper quadrant of the breast near the underarm.
Paye, et al. ed. Handbook of Cosmetic Science and Technology, Second Edition, 2007, Antibacterial Agents and Preservatives, p.225