Nobody knew they had bad breath. A few who did were not bothered by it. That was till Lambert Pharmacal Company decided to market a diluted version of their surgical antiseptic as a mouthwash named Listerine and the company became a clear and early example of a larger trend: marketing campaigns inventing problems that the product is alleged to solve.
Freakonomics says this for Listerine
"Listerine, for instance, was invented in the nineteenth century as powerful surgical antiseptic. It was later sold, in distilled form, as both a floor cleaner and a cure for gonorrhea. But it wasn't a runaway success until the 1920s, when it was pitched as a solution for "chronic halitosis"- a then obscure medical term for bad breath. Listerine's new ads featured forlorn young women and men, eager for marriage but turned off by their mate's rotten breath. "Can I be happy with him in spite of that?" one maiden asked herself. Until that time, bad breath was not conventionally considered such a catastrophe. But Listerine changed that. As the advertising scholar James B. Twitchell writes, "Listerine did not make mouthwash as much as it made halitosis." In just seven years, the company's revenues rose from $115,000 to more than $8 million."