For most of human history, people did very little to rein in their bodys ripe aroma. If anything, they washed periodically or tried to hide their odour by masking it with strong fragrances. All that changed just over 100 years ago with the invention of deodorants and antiperspirants. These products differ from perfumes because they dont just cover human stink; they thwart its production. Today, annual worldwide sales of deodorants and antiperspirants top $18 billion. Deodorants typically include antiseptic ingredients that kill or disable bacteria living in the armpit. That regions warm and moist environment is an optimal habitat for corynebacteria and other sweat-eating microorganisms. These tiny life-forms feast on perspiration produced by armpit sweat glands, generating stinky waste by-products such as trans-3-methyl-2-hexenoic acid. This compound is responsible for the characteristic odour of human sweat, says George Preti, a chemist at Monell Chemical Senses Centre who specialises in perspiration research. Whereas deodorants try to kill the odour-producing culprits, antiperspirants block sweat pores, thereby preventing the flow of nutrients to armpit microorganisms. Both products typically include a bit of perfume as backup. The first patents for deodorants were filed in the 1860s, when antiseptic entrepreneurs looked for new surfaces to clean with newly discovered sanitising agents such as ammonium chloride, sodium bicarbonate, and even formaldehyde, which is now known to be a carcinogen. In 1888, the first trademarked deodorant, called Mum, hit the U.S. market. In the book Antiperspirants and Deodorants, cosmetic care consultant Karl Laden asserts that Mums active ingredient was zinc oxide, which is still commonly found in deodorants. Current deodorant ingredients vary vastly, from antibiotics to citronella oil. All are intended to control bacterial growth. The huge array of active ingredients in deodorant contrasts starkly with those found in antiperspirants. From the get-go, antiperspirants have relied on aluminium salts to stop the flow of sweat. Patent applications for antiperspirants also first appeared in the late 1800s, with the first trademarked antiperspirant, called Everdry, arriving in the U.S. in 1903, according to Laden. Everdrys active ingredient was aluminium chloride, a salt that forms aggregates in sweat pores and blocks them. In the subsequent century, antiperspirant makers have used aluminium formate, aluminium chlorohydroxide, and aluminium zirconium tetrachlorohydrate. Furthermore, antiperspirants typically include some ingredients to counter bacteria and are thus often an antiperspirant-deodorant hybrid. In the 1970s, some researchers began to fear that aluminium in antiperspirants could lead to Alzheimers disease. Subsequent studies have convinced the American Alzheimers Association, a patient advocacy group, and the Food & Drug Administration, which regulates antiperspirants, that the connection between aluminium in antiperspirants and neurodegeneration is a myth. Aside from active ingredients, the way that deodorants and antiperspirants are applied to the armpit has evolved dramatically since their inception. The same holds true for the solvents in which the active ingredients are dissolved or suspended. Early antiperspirants suspended their active ingredient in alcohol or, more often, acids, and they had to be swabbed with cotton balls on the armpit. These formulations were slow to dry and prone to irritating skin and ruining clothing. Likewise, early deodorants were often sold as creams, which were rubbed by hand on the armpit, often leaving these zonesand any clothingunappealingly greasy. Inspired by the ballpoint pen, roll-on deodorants were invented in the 1940s. Sticks, gels, and aerosols emerged in the decades thereafter. Although these new deodorant and antiperspirant products improved the aesthetics and ease of application, the biggest nonactive ingredient innovation came in the 1970s, when quick-dry cyclomethicones, also known as methylsiloxanes, hit the market, Laden notes. Cyclomethicone solvents are now widespread in many antisweat products because they dont irritate skin and they evaporate quickly, leaving behind the deodorant or antiperspirants active ingredient but no greasiness or stickiness. Cyclomethicones are, however, under regulatory scrutiny in Europe because of concerns that the moleculeswhich are also widely used in hand creams, hair conditioners, makeup, and other personal care productsmay bioaccumulate in the environment. In recent decades, makers of deodorants and antiperspirants have begun encapsulating active ingredients in time-release polymer enclosures so the products last longer. Many deodorant and antiperspirant companies have also been developing additives that specifically block the action of bacterial enzymes responsible for turning odourless sweat into an unpleasant stench, Laden notes. Preti and his colleagues have helped create additional ingredients that distract the nose of nearby people from stinky sweat smells. Theyve found a collection of pleasingly fragrant molecules that are similar in shape to some of the unpleasant odours in human sweat. These mimics physically occupy the receptors in the nose that are normally devoted to detecting the offensive odour molecules. In human tests, mens noses were easier to trick than womens. Sweating may be an inescapable part of being human, but the past 100 years have shown that people who want to restrain their armpit aroma have abundant options for doing so.
Chemical & Engineering News, 2 July 2012 ;http://pubs.acs.org/cen/news ;