“Halitosis—Makes you Unpopular” was the headline of Listerine's campaign. Originally a disinfectant, invented for medical usage on the battlefield, the brown liquid had also been marketed as a floor cleaner. But in the 1920s, under new management, the manufacturer presented it as a cure for a devastating problem countless Americans were unwittingly afflicted with. “No matter how charming you may be or how fond of you your friends are, you cannot expect them to put up with halitosis (unpleasant breath) forever. They may be nice to you—but it is an effort.” … The ominously clinical-sounding “halitosis” was a largely unheard of word when Listerine introduced it. But they rightly gauged the human psyche and the tenor of the times by stirring fears about a problem everyone encounters in others from time to time without comment. Directing this kind of scrutiny to it can't help but make one wonder about one's own breath (as you yourself may now be doing). The campaign was a masterpiece of demand engineering, and between 1922 and 1929, the Listerine company's annual earnings rose from $115,000 to over $8 million.

Tim Wu, The Attention Merchants, loc. 190