Where there's spice, there's a loyal shopper.

New understanding about how people who love spicy foods eat—and shop—is fueling the latest wave in making packaged foods hotter.

"You get endorphins when you eat something really spicy," which feels adventurous to flavor-seeking eaters, says Krista Lorio, senior manager of consumer insights for General Mills Inc., which owns Cheerios, Betty Crocker and other brands. That experience can "create a lot of loyalty," she says. The company recently started selling Helper Bold, a version of its boxed line of pasta that comes in Firehouse Chili Macaroni and other flavors.

Spicy food can act as a badge of authenticity for some people, which also makes them loyal, say food companies.

But "the gatekeeper"—General Mill's term for a household's primary cook and shopper—needs to have at least heard of a product's main ingredients to consider buying it, says Ms. Lorio. Most shoppers didn't recognize the term hatch green chilies when the company tested ideas for new Old El Paso cooking sauces and frozen meals, for example. (They did know chipotle, chili, and roasted garlic.)