Before there were vapes, there was sulfanilamide. One of the first great medicines of the antibiotic era, sulfanilamide was a miracle drug at a time when curing pneumonia with a quick trip to the pharmacy seemed akin to walking on water. When a sweet, raspberry-flavored liquid version appeared in stores in early September of 1937, it was a no-brainer prescription for doctors whose sick young patients were still picky enough they might reject even Jesus himself if he returned in the form of a bitter-tasting pill.

By the end of October, more than 100 of those patients had died and regulators were scrambling to figure out why.

All of this has happened before, and all of this will happen again. Today, medical experts and federal regulators are struggling to understand a mysterious lung disease linked to the use of electronic cigarettes. As of Sept. 17, 530 people have been diagnosed across the country, seven of whom have died. Neither the Centers for Disease Control and Prevention nor the Food and Drug Administration can definitively say what is causing the illness or why a device that was supposed to help people stop smoking cancer-causing cigarettes has, itself, turned deadly.

Regardless of why e-cigs have turned toxic, historians and consumer law advocates see lessons in the sulfanilamide disaster of 1937 — ones that go beyond the obvious surface similarities of poisonous, fruit-flavored liquids. Both cases highlight the way consumer protections in this country are reactive, cropping up in response to disease and death, rather than preventing it.

“There’s insanely heartbreaking letters from these doctors who had prescribed [sulfanilamide elixir] and then watched kids die,” said Deborah Blum, author of “The Poison Squad,” a book about the founding of the FDA. Those deaths were painful and prolonged, stretching out over days and weeks of convulsions, nausea, kidney failure and stupor. “No one had any idea what was going on. The FDA was desperately sending scientists around the country,” she told me.

Eventually, a Kansas City FDA inspector confirmed that eight children and one adult who died in his area had all taken the same medication, prepared by S.E. Massengill Co., based in Tennessee. Chemists broke the concoction down, molecule by molecule, and discovered that Massengill had blended its antibiotic with diethylene glycol. In other words, it had taken medicine and raspberry flavoring and mixed it up with antifreeze.

A similarly desperate cross-country investigation is happening now with the vaping-related lung deaths, but pinning down a cause is proving harder in this case. There’s no tell-tale chemical turning up in every sample. Eighty-four percent of the 53 patients whose cases were reported in a study published by the New England Journal of Medicine did admit to using e-cigarette pods that contained THC, the chemical in pot that gets you high. But that’s a small and geographically isolated sampling. Other than vaping, itself, there’s no single behavior all the victims share. There’s no Massengill in our modern story, no single company glowing ominously like a lit cigarette in a dark alley.

More frustratingly, said Anne Schuchat, principal deputy director of the CDC, there are several reasons why patients might not be giving doctors an accurate account of what they’ve used and how. Some are too sick. Some might not want to talk to the government about their THC use. The state of Illinois has begun an anonymous survey of healthy e-cigarette users, hoping to spot some differences between the people who have gotten sick and those who haven’t. It’s likely there’s more than one poison at play.

Meanwhile, there’s also not a clear trail of what was sold, who sold it and whom they sold it to. That was true in the 1937 disaster, as well. But investigators knew Massengill had made the product and tried to recall it. E-cigarettes, in contrast, are more of a mom and pop affair. Lots of people are making and selling e-liquids and some of them are amateurs, working off the books. That’s especially true of liquids containing THC.

But this isn’t just about a contaminated black market. Even the e-liquids with the most professional pedigrees haven’t been subject to stringent safety regulations, said Desmond Jensen, an attorney with the Public Health Law Center at the Mitchell Hamline School of Law. In 1937, Blum said, pro-regulation advocates had already been warning people for years that there were too many loopholes in FDA rules. And the same is true in this case. There were no FDA regulations at all on e-cigarettes until 2016, and the regulations that exist now are more like swiss cheese than solid cheddar, Jensen said.

“When you say a product is regulated, the average person thinks about pesticides, food or drugs,” he told me. “There’s someone making sure it’s not tainted, or making sure it won’t make us sick. That’s not what it means here.” Instead, the FDA requires sellers and manufacturers of e-cigarettes and e-liquids to register with and disclose ingredients to the agency. But that isn’t the same as quality or safety testing, Jensen said. And a lot of companies haven’t registered in the two years those regulations have been in effect. Safety testing regulations do exist — but their implementation keeps getting scooched back under pressure from vaping companies. Currently, products that were on the market before 2016 won’t have to be reviewed for safety until May of 2020. Manufacturers who don’t sell directly to consumers haven’t had to register or disclose ingredients at all.

In 1937, it was completely legal to sell antifreeze-sweetened medicine to children. The only crime the Massengill company could be charged with was misbranding its liquid as an “elixir,, which legally had to contain alcohol, rather than as a “solution,” Blum said. (In fact, this distinction was the only thing that allowed the FDA to get involved and recover the tainted medicine from consumers to begin with.) The sulfanilamide disaster changed everything about consumer safety. Within a year, we had a new Food, Drug, and Cosmetic Act that, for the first time, gave the FDA the power to demand companies prove a drug was safe before it could be sold.

And that’s effectively the problem we have with e-cigarettes today, Jensen said. The pre-sale approval process exists, but there are thousands of products it doesn’t yet apply to. Meanwhile, it’s legal to sell e-cigarette liquids that contain chemicals we’ve banned as food additives, or that contain chemicals nobody has even thought to list in a database because they form in the package after the ingredients have been mixed together. And while states have begun to ban flavored e-liquids in response to the lung disease outbreak (and the federal government may do the same), that doesn’t solve consumer protection problems that aren’t related to flavoring, such as liquid nicotine that contains far more of the drug than is claimed on the label, or e-cigarette devices manufactured in China that aren’t being held to any kind of safety standards.

But it’s no real surprise we’ve ended up here, said Marian Moser Jones, a public health professor at the University of Maryland. Our laws aimed at stopping products from poisoning people have usually come in reaction to deaths and illness, rather than before.

Ultimately, Moser Jones said, you can look on both historical poisoning cases and the current vaping crisis as a direct result of consumer product safety policy that often favors a right to sell over a right to know that what is being sold is safe. “In other countries there’s less of a question about whether the government has a right to interfere with commerce,” she said. When the careful balance between retailers rights and consumers tips too far to one side, people die.

CORRECTION (Oct. 1, 12:43 p.m.): An earlier version of this story misidentified Marian Moser Jones’s department at the University of Maryland. She is a public health professor, not a professor of history and ethics.