Meredith DelPrete, 10, holds the type of magnet she accidentally swallowed. (Astrid Riecken/FOR THE WASHINGTON POST)

When a 9-year-old old boy accidentally swallowed several tiny round magnets in 2010, regulators turned to one of the most familiar tools in their arsenal: warning labels.

The boy wasn’t hurt, but other cases kept surfacing, sometimes forcing kids into emergency rooms. The government learned of eight more incidents that year, another 17 last year and 25 this year — even after launching a public-service campaign warning that swallowing two or more of the balls can damage the digestive tract.

In response, the Consumer Product Safety Commission did what it has rarely done before. It gave up on the warnings and proposed an outright ban.

The push last month to take this category of BB-sized magnets off the market signals a broader rethinking of an approach that Washington has long relied on to flag the hazards of everything from cigarettes to plastic bags.

The agency also successfully pushed for a recall of 4 million Bumbo baby seats last month after concluding that the warnings on those chairs did not adequately prevent the seats from being used in ways that could result in children falling and injuring themselves.

“What you’re getting into now is as much about the agency’s philosophy on how to deal with risk as it is about safety,” said Mike Gidding, a former CPSC attorney who specializes in product safety cases.

CPSC Chairman Inez Tenenbaum said she’s steering the agency in a new direction by trying to prevent deaths instead of just reacting to them. “I have made it clear to our staff that all of our regulatory options should be on the table when we seek to protect consumers from harm,” Tenenbaum said in a statement.

Some of the earliest federally mandated warnings came in 1927 when Congress passed a law requiring “poison” labels on household products containing certain caustic or corrosive substances, according to a report by Exponent Failure Analysis Associates, a consulting firm. Warnings on drugs, medical devices and cosmetics followed a decade later.

But a warnings boom took place in the 1960s, giving rise to some of today’s most familiar labels, the report said. That’s when words like “danger” and “flammable” and “keep out of reach of children” started appearing on entire categories of products with hazardous substances. It’s also the decade that Congress mandated warnings for cigarettes.

Today, warnings are so pervasive that they’ve become a nearly meaningless safety tool in some areas, more useful in protecting manufacturers against legal liability than in guarding consumers from harm, according to David Egilman, a clinical professor at Brown University’s family medicine department who has researched industry’s influence on warnings.

“If everything you pick up has a warning on it, you’re going to instinctively ignore all warnings,” Egilman said. “That’s the real problem.”

It’s the classic “cry wolf” situation, said Richard Thompson, a psychology and biological sciences professor at the University of Southern California. People exposed to the same stimulus without consequences are less likely to pay attention, he said.

“It’s a universal phenomenon we see in all animals,” said Thompson, a member of the National Academy of Sciences. “If you touch the sea anemone, its tentacles retract. Touch it again, and it contracts less. Touch it a few more times and it stops responding.”

To deal with these challenges, the CPSC sometimes asks companies to rework their warning labels or display them more prominently. It occasionally demands a design change, as it did with Bumbo seats when the warning labels alone failed to curb injuries.

The Bumbo warning labels, which had been developed in coordination with the CPSC, cautioned against placing the molded foam seats on raised surfaces. Yet babies continued to squirm out of the seats and fall, sometimes fracturing their skulls, even with the seats on the floor. Last month, Bumbo recalled the chairs and offered restraint belts that it created with input from the CPSC, the company said. Even with the belt, the firm still warns against using the seats on raised surfaces.

It is rare for the agency to go beyond warning labels and design fixes. That’s why the magnet issue has caused a stir. The agency is pushing to ban these types of magnets, and 11 firms that sell them have agreed to stop doing so. But two have refused, including the distributor of Buckyballs, the dominant player in the U.S. market since 2009.

Nancy Nord, a CPSC commissioner, has urged the agency to think through the broader implications of the proposed ban, arguing that it is too early to tell if the warnings are ineffective because the magnets — and their warnings — are relatively new to the market. Not giving the warnings a chance to work “would eviscerate many of the safety standards that the Commission (and Congress) have deemed acceptable,” Nord wrote in a statement.

Maxfield and Oberton, the distributor of Buckyballs, says it should not be penalized for misuse of its products, which are marketed as adult desktop toys. It also says the agency’s reasoning undermines its long-standing support for warnings on more dangerous items, such as balloons, fireworks and button batteries.

Regulators said that while warning labels are effective for some products, they aren’t working with these magnets.

It’s not clear what would make the magnets safer. In public documents, CPSC staff said the balls pose hidden dangers because they appeal to children in ways that are not obvious to caregivers — unlike “predictably hazardous products like skateboards, knives or balloons.” Kids, for instance, have stuck them on their braces and used them to mimic tongue piercings.

While child-resistant carrying cases could be designed, they most likely would not work, regulators said. Single cases can come with hundreds of magnets inside, making it tough for parents to detect the loss of individual balls and easy for kids to share. The small size of the magnets precludes warnings on each one.

For decades, regulators have concluded that the best way to address a safety hazard in a product is to have it redesigned to remove the danger. Next best is adding safeguards — for instance, requiring that bottles of medication have child-resistant caps.

Warning labels have been a strategy of last resort because people have to notice, read and understand them.

One way to win a consumer’s attention is to rotate the message on labels or add images to the warnings because the human brain responds to novelty, several psychology experts said. These techniques have been used in cigarette warnings in the United States and abroad, often meeting objections from the tobacco industry. A law directing the Food and Drug Administration to add jarring anti-smoking images to cigarette packs has been tied up in a court battle since 2009.

Even when a warning is attention grabbing, however, what ultimately matters is whether a person is motivated to comply with it, said Sam Glucksberg, emeritus professor of psychology at Princeton University.

“If you’re addicted to nicotine, you can know all you need to know about the dangers of nicotine,” Glucksberg said. “But there’s a conflict between the health issue and the addiction.”