In recent years, one bright spot in an otherwise lackluster market for packaged foods, beverages and consumers products has been merchandise promoted as “natural.”

Consumers, increasingly wary of products that are overly processed or full of manufactured chemicals, are paying premium prices for natural goods, from fruit juices and cereals to shampoos and baby wipes.

But as a spate of lawsuits and consumer advocacy efforts show, one person’s “natural” is another person’s methylisothiazolinone.

The problem, consumer groups and even some manufacturers say, is that there is no legal or regulatory definition of what “natural” is.

The debate in many ways echoes the tussling in the 1990s over the word “organic,” when foodmakers played fast and loose with the term and frustrated consumers tried to make sense of it all.

The U.S. Department of Agriculture, tasked with creating an “organic” program, was pestered by consumers, farmers, manufacturers and states as it developed a definition, guidelines and a certification process.

Today, while regulators are weighing whether to define the term “natural,” the lack of clarity over the last decade has resulted in a freewheeling, and litigious, environment.

On one side are companies eager to cash in on consumers’ willingness to pay higher prices for natural products by slapping “all natural” labels on them. At times, the claims have stretched the limits of credulity — like “All Natural” 7UP, Pop-Tarts “Baked With Real Fruit” and Crystal Light “Natural” lemonade. (Some labels like these were eventually changed.)

On the other side are a cadre of plaintiffs lawyers — nicknamed “the Food Bar” — that have filed more than 300 lawsuits seeking class-action status in the last three years. Those claims involve allegations of misrepresentations, just on food labels, of the term “natural” and other descriptions.

And, increasingly, the lawsuits are moving beyond food and focusing on consumer goods like baby wipes and cleaning products.

Among the brands that have faced legal challenges are several that have long promoted their use of natural ingredients: Tom’s of Maine antiperspirants and toothpastes, the Honest Co.’s laundry detergent and dish soap, Annie’s Homegrown salad dressings, Breyers and Ben & Jerry’s ice cream, Aveeno face moisturizers and Seventh Generation dish soap.

“The lawsuits you see are only a fraction of the claims that are made,” said David T. Biderman, a partner at Perkins Coie who defends food companies in class-action lawsuits. Behind the scenes, Biderman said, plaintiffs’ lawyers are sending letters to companies and threatening to file lawsuits over labels they argue are misleading or violate consumer protection laws. Those letters, Biderman said, are often rejected, go away or are resolved with a small payment.

Whether the lawsuits are necessary, or a nuisance, depends on whom you ask.

Proponents say that, in lieu of clear regulation, consumers have been protected by these lawsuits, pointing to a number of cases in which manufacturers have altered their labels. General Mills, which faced at least two federal lawsuits claiming that its Nature Valley granola bars contained artificial ingredients, replaced labels that once read “100% Natural” to say they are “Made With 100 percent Natural Whole Grain Oats.”

Corporations, lawyers say, have been reluctant to allow a case to go to trial and risk having a legal definition of “natural” emerge — which might set standards companies would have to meet. As a result, the bulk of the lawsuits filed over the last decade have been settled, dismissed or, more recently, stayed by judges who hope regulators will step in with a definition.

Kim Richman, a plaintiffs lawyer, said his clients, which include consumers and nonprofit groups, “engage in socially conscious litigation to level the playing field against corporate America as government oversight increasingly falls short.”

But critics say a big chunk of the settlement money lands in the pockets of the plaintiffs’ lawyers, and does not financially benefit consumers.

Critics also argue that some lawyers are robo-filing lawsuits — cut-and-pasting nearly identical allegations into complaints against multiple companies — and in the process are bringing head-scratching cases that risk undermining the credible ones.

A federal judge tossed a case a few years back, for instance, after concluding that reasonable consumers would understand that the “crunchberries” in Cap’n Crunch cereal were not real fruit. But another judge in California last year refused to dismiss a case against Krispy Kreme, which claimed that consumers were denied the health benefits found in raspberries because the company’s “raspberry-filled” doughnuts did not include real fruit. The plaintiff later dropped the lawsuit.

A number of more recent cases involve allegations that products labeled natural were misleading because they contained small amounts of materials linked to genetically modified organisms. In December, a New York federal court judge dismissed a lawsuit claiming that Dannon yogurt was falsely labeled natural because the cows may have been given genetically modified feed.

The new focus in litigation away from the ingredients in the food to the actual food chain — how the crop was grown or what the animals were fed — may undermine the original goal of the lawsuits, which was addressing nutritional concerns, some experts say.

“We’re really getting into splitting hairs about what is natural and what’s not,” said Maia Kats, the director of litigation for the Center for Science in the Public Interest, a public advocacy group has been involved in a handful of lawsuits over so-called natural products.

Stuck in the middle of this natural-or-not morass are consumers. Unable to trust the labels lining store shelves, shoppers are left with little choice but to examine the small type on the back of the box and try to decipher terms like methylisothiazolinone, a synthetic preservative found in some personal- and skin-care products.

A survey of consumers in 2015 by Consumer Reports magazine showed that at least 60 percent of respondents believed “natural” on packaged and processed foods meant they contained no artificial colors or ingredients and no genetically modified materials.

“About two-thirds of consumers surveyed think that natural on a food package means no pesticides were used,” said Charlotte Vallaeys, a senior policy analyst with Consumers Union, the advocacy division of Consumer Reports. “They’re confusing it with organic,” which prohibits nearly all pesticides from use on food products.

But when it comes to commonly used terms like “natural” or even “healthy,” the various agencies that oversee food and beverages and advertising have been slow to come up with definitions.

In late 2015, the U.S. Food and Drug Administration sought feedback from consumers and the industry on whether it should define and regulate the word “natural” on food labeling.

More than 7,600 comments flooded in. Some consumers wanted the word banned from all food labeling. Others asked that the term be defined simply.

“We recognize that consumers are trusting in products labeled ‘natural’ without clarity around the term,” Dr. Scott Gottlieb, the commissioner of the FDA, said in an emailed statement. “Consumers have called upon the FDA to help define the term ‘natural’ and we take the responsibility to provide this clarity seriously. We will have more to say on the issue soon.”

Most agencies argue they lack the resources to police products that, while not necessarily truthful in their labeling, do not appear to be causing harm to consumers, either. The class-action lawsuits, for the most part, seek reimbursement in the price difference between the “natural” product and its less-natural competition.

Apart from food, the regulation of claims in the advertising of shampoos and laundry detergent gets even murkier.

In 2012, when the Federal Trade Commission updated its Green Guides, a road map to help marketers avoid making environmental claims that could mislead consumers, it did not define the word “natural.” Laura Koss, a lawyer in the division of enforcement, said the commission received insufficient consumer feedback about the term when it sought comment.

Still, lawyers say that until regulators come up with a definition, the not-so-natural dance between consumers, manufacturers and lawyers will continue.

“You’ve got a lot of companies, in the absence of clear standards, willing to take the class-action risk because there is so much consumer demand for products that are marketed as natural,” said Randal M. Shaheen, a lawyer with Venable who defends corporate advertising and marketing claims. “But if you’re a consumer who is really passionate about, for example, not giving your kids high-fructose corn syrup, you should read the label to see how it is sweetened.”

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