However, when his old friend approached Hopkins about Pepsodent, the ad man expressed only mild interest. It was no secret that the health of Americans’ teeth was in steep decline. As the nation had become wealthier, people had started buying larger amounts of sugary, processed foods. 2.2 When the government started drafting men for World War I, so many recruits had rotting teeth that officials said poor dental hygiene was a national security risk. Yet as Hopkins knew, selling toothpaste was financial suicide. There was already an army of door-to-door salesmen hawking dubious tooth powders and elixirs, most of them going broke. The problem was that hardly anyone bought toothpaste because, despite the nation’s dental problems, hardly anyone brushed their teeth

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The secret to his success, Hopkins would later boast, was that he had found a certain kind of cue and reward that fueled a particular habit. It’s an alchemy so powerful that even today the basic principles are still used video game designers, food companies, hospitals, and millions of salesmen around the world. Eugene Pauly taught us about the habit loop, but it was Claude Hopkins that showed how new habits can be cultivated and grown. So what, exactly, did Hopkins do? He created a craving. And that craving, it turns out, is what makes cues and rewards work. That craving is what powers the habit loop.

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After the campaign launched, a quiet week passed. Then two. In the third week, demand exploded. There were so many orders for Pepsodent that the company couldn’t keep up. In three years, the product went international, and Hopkins was crafting ads in Spanish, German, and Chinese. Within a decade, Pepsodent was one of the top-selling goods in the world, and remained America’s best-selling toothpaste for more than thirty years. 2.10, 2.11 Before Pepsodent appeared, only 7 percent of Americans had a tube of toothpaste in their medicine chests. A decade after Hopkins’s ad campaign went nationwide, that number had jumped to 65 percent. 2.12 By the end of World War II, the military downgraded concerns about recruits’ teeth because so many soldiers were brushing every day. “I made for myself a million dollars on Pepsodent,” Hopkins wrote a few years after the product appeared on shelves. The key, he said, was that he had “learned the right human psychology.” That psychology was grounded in two basic rules: First, find a simple and obvious cue. Second, clearly define the rewards.

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“Consumers need some kind of signal that a product is working,” Tracy Sinclair, who was a brand manager for Oral-B and Crest Kids Toothpaste, told me. “We can make toothpaste taste like anything—blueberries, green tea—and as long as it has a cool tingle, people feel like their mouth is clean. The tingling doesn’t make the toothpaste work any better. It just convinces people it’s doing the job.”

 

“Foaming is a huge reward,” said Sinclair, the brand manager. “Shampoo doesn’t have to foam, but we add foaming chemicals because people expect it each time they wash their hair. Same thing with laundry detergent. And toothpaste—now every company adds sodium laureth sulfate to make toothpaste foam more. There’s no cleaning benefit, but people feel better when there’s a bunch of suds around their mouth. Once the customer starts expecting that foam, the habit starts growing.” Cravings are what drive habits. And figuring out how to spark a craving makes creating a new habit easier. It’s as true now as it was almost a century ago. Every night, millions of people scrub their teeth in order to get a tingling feeling; every morning, millions put on their jogging shoes to capture an endorphin rush they’ve learned to crave.