Listerine Mouthwash Allegedly Increases Cancer-Causing Bacteria
Class action claims Johnson & Johnson and Kenvue concealed that daily use of Listerine Cool Mint causes proliferation of bacteria linked to multiple deadly cancers, exposing millions of consumers to undisclosed health risks.
A California consumer alleges that Listerine Cool Mint Antiseptic Mouthwash, manufactured by Johnson & Johnson and later Kenvue, causes the proliferation of bacteria linked to oral, colorectal, pancreatic, breast, and other deadly cancers when used as directed. Despite marketing the product as killing 99% of germs, the companies allegedly concealed studies showing three months of normal use significantly increases Fusobacterium nucleatum and Streptococcus anginosus in users’ mouths. The lawsuit claims defendants violated federal drug safety laws and California consumer protection statutes by failing to warn millions of daily users about these cancer-associated bacteria.
If you used Listerine Cool Mint regularly, you may have been exposed to undisclosed cancer risks while the manufacturers profited from your trust.
The Allegations: A Breakdown
| 01 | Defendants marketed Listerine Cool Mint as killing 99% of germs that cause bad breath, plaque, and gingivitis, while concealing that regular use causes proliferation of Streptococcus anginosus and Fusobacterium nucleatum, bacteria closely associated with oral cancer, head and neck cancer, colorectal cancer, pancreatic cancer, esophageal cancer, gastrointestinal cancer, and breast cancer. | high |
| 02 | A 2024 study found that after three months of normal Listerine Cool Mint use, F. nucleatum and S. anginosus became significantly more abundant than baseline levels, directly contradicting the product’s germ-killing marketing claims. | high |
| 03 | Defendants directed consumers to use the product twice daily for 30 seconds on their website and packaging, establishing a usage pattern that the complaint alleges causes the bacterial proliferation linked to deadly diseases. | high |
| 04 | The product packaging warns only about use by children under 12 and swallowing, but nowhere discloses that recommended daily use causes proliferation of cancer-causing bacteria, misleading consumers into believing the product is safe when used as directed. | high |
| 05 | Defendants marketed Listerine as providing a fresher and cleaner mouth than brushing alone and as the most extensively tested OTC mouthwash with over 50 clinical trials, yet allegedly failed to disclose negative findings about bacterial proliferation from their extensive testing. | high |
| 06 | F. nucleatum has been shown to survive longer than other bacteria under acidic gut conditions, suggesting these bacteria can travel from the mouth through the digestive tract, and oral concentration of this bacteria predicts colon cancer prognosis. | high |
| 07 | S. anginosus has been linked to gastro-intestinal cancer and colorectal cancer, and both S. anginosus and F. nucleatum were found to be predominant in patients suffering from oral squamous cell carcinoma. | high |
| 08 | The proliferation of these bacteria causes oral dysbiosis with downstream effects on various cancers, as published literature shows oral and gastrointestinal microbiomes play a significant role in cancers that are established, promoted, and protected by bacterial imbalances. | high |
| 01 | The product violates the Federal Food, Drug, and Cosmetics Act by being a misbranded drug because its labeling is false or misleading by omitting that use causes proliferation of cancer-causing bacteria, a material fact regarding consequences of customary use. | high |
| 02 | Federal regulations require manufacturers to revise labels to include a warning as soon as there is reasonable evidence of an association of a serious hazard with a drug, and to maintain and update labeling with new safety information, yet defendants failed to do so. | high |
| 03 | The product fails to meet OTC drug requirements because it is not generally recognized as safe and effective when it causes proliferation of bacteria associated with deadly cancers, rendering it an unapproved new drug that cannot be legally marketed. | high |
| 04 | Defendants became aware of health risks by June 2024 when a scientific study finding that Listerine causes proliferation of cancer-causing bacteria was published and widely reported, yet continued selling without updated warnings. | high |
| 05 | The product violates California Sherman Food, Drug, and Cosmetic Law by failing to include necessary warnings about bacterial proliferation despite being marketed as a health product for daily use. | medium |
| 06 | Defendants touted extensive clinical testing including 50 trials with over 30 lasting six months or longer, and fifteen 6-month studies in 3,203 subjects over 20 years, giving them ample opportunity to detect the bacterial proliferation risk yet concealing findings. | high |
| 01 | The oral rinse market was valued at $6.51 billion in 2021 and is expected to expand at 7.1% annual growth from 2022 to 2030, reaching $15.7 billion by 2032, giving defendants enormous financial incentive to conceal health risks that could damage Listerine’s market position. | high |
| 02 | Defendants knew that disclosing the Product causes proliferation of cancer-causing bacteria would lead consumers to stop purchasing entirely or pay significantly less, directly threatening their multi-billion dollar revenue stream from the lucrative mouthwash market. | high |
| 03 | The concealment was material and intentional because people are concerned with health effects of products they put into their bodies, and defendants knew consumers purchase mouthwash to prevent oral disease and kill harmful bacteria, not to increase harmful bacteria prevalence. | high |
| 04 | Defendants made partial representations about germ-killing properties without disclosing the product causes proliferation of harmful bacteria, making the omission doubly misleading and calculated to maintain consumer trust while concealing known dangers. | high |
| 05 | Defendants failed to recall the product and continue to omit warnings about cancer-causing bacteria on packaging and labeling, prioritizing continued sales over consumer safety despite knowledge of the health hazard. | high |
| 06 | Consumers including the plaintiff purchased, purchased more of, and paid more for the Product than they would have had they known the truth, meaning defendants extracted premium pricing through material omissions about safety. | medium |
| 01 | Regular use of the Product causes proliferation of F. nucleatum, bacteria closely associated with oral cancer, head and neck cancer, colorectal cancer, pancreatic cancer, esophageal cancer, and breast cancer according to multiple scientific studies. | high |
| 02 | Studies link F. nucleatum with every stage of colon cancer, showing this bacteria increases as prognosis worsens and exacerbates cancer progression through influence of the microenvironment, with oral concentration predicting colon cancer outcomes. | high |
| 03 | S. anginosus has been linked to gastric inflammation, atrophy, tumorigenesis, gastro-intestinal cancer, and colorectal cancer, including cases where colorectal cancer was associated with S. anginosus bacteremia and liver abscesses. | high |
| 04 | Both S. anginosus and F. nucleatum were found to be predominant in patients suffering from oral squamous cell carcinoma, indicating these bacteria are markers of serious oral cancer conditions that defendants’ product allegedly promotes. | high |
| 05 | The bacterial proliferation creates oral dysbiosis with understood and studied downstream effects, as published literature confirms oral and gastrointestinal microbiomes play significant roles in various cancers established, promoted, and protected by bacterial imbalances. | high |
| 06 | F. nucleatum bacteria survive longer than other bacteria under acidic conditions like those in the gut, suggesting they travel from mouth to gut through the digestive tract, creating cancer risks throughout the gastrointestinal system. | high |
| 07 | Consumers who use the Product to prevent oral disease and kill harmful bacteria are unknowingly causing proliferation of bacteria associated with deadly cancers, receiving the opposite health effect from what the marketing promises. | high |
| 08 | A mouthwash product that causes proliferation of cancer-causing bacteria is unsafe for humans and entirely worthless, yet defendants continued marketing it as providing health benefits and a cleaner mouth. | high |
| 01 | Defendants had exclusive knowledge that the Product caused proliferation of cancer-causing bacteria that was not known or reasonably accessible to consumers, yet actively concealed this information to maintain sales and market position. | high |
| 02 | Consumers lack meaningful ability to test or independently ascertain whether a product causes proliferation of cancer-causing bacteria, especially at point of sale, making them entirely dependent on defendants’ honesty about health hazards. | high |
| 03 | Defendants knew consumers rely on warning labels on packaging to accurately disclose health risks, yet exploited this trust by providing only warnings about swallowing and child use while omitting the far more serious cancer-bacteria risk. | high |
| 04 | Despite federal regulations requiring manufacturers to update labeling with new safety information and revise labels when there is reasonable evidence of serious hazards, defendants failed to add any warnings about bacterial proliferation even after studies were published. | high |
| 05 | Defendants market the Product to health-conscious consumers using claims that appeal to safety concerns, making their omissions about cancer-causing bacteria particularly deceptive and an exploitation of consumer health priorities. | high |
| 06 | The misconduct was uniform and directed at all consumers who purchased the Product nationwide, with consistent marketing, advertising, packaging and labeling that concealed the bacterial proliferation across all channels and locations. | medium |
| 07 | Defendants created and authorized false, misleading, and deceptive advertisements, packaging, and labeling for the Product that promised germ-killing benefits while concealing that the product increases cancer-associated bacteria. | high |
| 01 | Consumers paid for a Product that was not what defendants represented and paid a premium price for a mouthwash they believed was safe and health-promoting, only to receive a product that allegedly increases cancer-causing bacteria. | high |
| 02 | Consumers were deprived of the benefit of their bargain because the Product they purchased was different from what defendants warranted and had less value than represented, as a cancer-risk-increasing mouthwash has no value. | high |
| 03 | The Product plaintiff and class members received was worthless because it has been shown to result in proliferation of cancer-causing bacteria, meaning they paid money for something with zero actual value. | high |
| 04 | If longtime Listerine users develop heightened risk of certain cancers or severe infections, medical interventions will be extensive and expensive, with working-class families least able to bear these costs, exacerbating wealth disparity. | high |
| 05 | Widespread health issues from the product could result in higher insurance premiums, with entire communities seeing rising healthcare costs to cover treatments for conditions defendants’ concealment allegedly caused. | medium |
| 06 | Serious illnesses from cancer-causing bacteria can force people out of work temporarily or permanently, causing financial instability and emotional hardship that falls on ordinary households while defendants retained their profits. | high |
| 07 | Consumers received moneys by defendants through deceptive marketing, with all class members paying money but not obtaining full value of the advertised Product due to misrepresentations and omissions about cancer-bacteria proliferation. | medium |
| 01 | Vulnerable populations including those with compromised immune systems and the elderly rely on additional oral-hygiene measures, meaning they may have unknowingly increased their risk of severe infections or cancers by incorporating Listerine into their daily regimen as recommended. | high |
| 02 | Ordinary consumers who use the Product to prevent oral disease are influenced by labels and warnings on products and lack of such warnings, trusting that well-known companies would disclose serious health risks on packaging. | high |
| 03 | Healthcare systems in low-income areas, already overburdened and underfunded, would struggle to manage an uptick in patients with advanced gastrointestinal or oral cancers resulting from undisclosed product dangers. | high |
| 04 | The economic burden of undisclosed dangers falls on society’s most vulnerable when the system fails to intervene, with corporate profits growing unabated while everyday people shoulder physical and economic costs. | high |
| 05 | Consumers such as plaintiff and class members are influenced by labels and warnings, and defendants knew if they had disclosed the bacterial proliferation, consumers would not have purchased the product at all or paid less for it. | medium |
| 06 | The omitted information about cancer-causing bacteria relates to an unreasonable safety hazard, making the concealment particularly harmful to communities who trusted the product’s safety based on its ubiquity and brand reputation. | high |
| 01 | Defendants marketed the Product by promising to kill 99% of germs that cause bad breath, plaque, and gingivitis, using health-focused claims that directly contradict the concealed reality of cancer-bacteria proliferation. | high |
| 02 | Defendants promoted the Product as providing a fresher and cleaner mouth than brushing alone, using positive health messaging to build trust while concealing that regular use increases dangerous bacteria linked to deadly diseases. | high |
| 03 | The company’s website specifically directs consumers to use the product twice per day for 30 seconds, establishing the precise usage pattern that allegedly causes the bacterial proliferation defendants failed to disclose. | high |
| 04 | Defendants represented that Listerine is the most extensively tested OTC mouthwash examined in more than 50 clinical trials with over 30 lasting six months or longer, using claims of rigorous testing to build consumer confidence while concealing negative findings. | high |
| 05 | Marketing materials tout proven safety and tolerability in clinical studies and safety supported by fifteen 6-month studies in 3,203 subjects over 20 years, using their own extensive testing as a trust-building tool while allegedly hiding what that testing revealed. | high |
| 06 | The Product’s prominent labeling about killing 99% of germs makes affirmative statements promising consumers the Product will eliminate harmful bacteria, making the concealment of bacterial proliferation doubly misleading and calculated. | high |
| 07 | Defendants sell the Products in all 50 states on their website and through various distributors and retailers, marketing them in a consistent and uniform manner that conceals the cancer-bacteria risk from millions of consumers nationwide. | medium |
| 01 | Defendants made, and continue to make, affirmative false statements and misrepresentations to consumers while omitting that the Product causes proliferation of cancer-causing bacteria, conduct that is ongoing and continuing. | high |
| 02 | A mouthwash product that poses serious health risk to consumers by causing proliferation of cancer-causing bacteria has no value and is in no way safe for humans, yet defendants continued selling it as a health-promoting product. | high |
| 03 | The defects in design or manufacture of defendants’ Product were not reasonably detectible to consumers, who had no realistic ability to discern the bacterial proliferation until they learned about it from scientific studies. | high |
| 04 | Defendants’ false, misleading, and deceptive misrepresentations and omissions are likely to continue to deceive and mislead reasonable consumers and the general public as they have already deceived and misled plaintiff and class members. | high |
| 05 | Prospective injunctive relief is necessary because defendants’ conduct is ongoing and continuing, especially given plaintiff’s desire to purchase the Product in future if she can be assured it will not cause proliferation of cancer-causing bacteria. | medium |
| 06 | The misconduct demonstrates that defendants engaged in unfair, fraudulent, or unlawful business practices with respect to advertising, marketing, and sale of their Product, violating multiple California and federal consumer protection laws. | high |
Timeline of Events
Direct Quotes from the Legal Record
“Defendants market and sell the Product without warning consumers that regular use of the Product causes the proliferation of certain bacteria, including but not limited to Streptococcus anginosus (S. anginosus) and Fusobacterium nucleatum (F. nucleatum), each of which can cause severe invasive infections and have been closely associated with multiple potentially deadly cancers, including oral cancer, head & neck cancer, colorectal cancer, pancreatic cancer, esophageal cancer, gastro-intestinal cancer, and breast cancer.”
💡 This establishes that defendants marketed a product as health-promoting while concealing its association with multiple deadly cancers.
“A recent study found that after three months of normal use, Listerine Cool Mint greatly affected the microbiome composition. Specifically, after the three-month period, F. nucleatum and S. anginosus were found to be significantly more abundant than at the measured baseline of patients.”
💡 This proves that recommended daily use directly causes proliferation of bacteria linked to cancer, contradicting marketing claims.
“Fusobacterium nucleatum is a bacteria that is closely associated with oral cancer, head & neck cancer, colorectal cancer, pancreatic cancer, esophageal cancer, and breast cancer. Studies have been conducted that closely link this particular bacteria with colorectal cancers, but also link oral concentration of this bacteria with prediction of colon cancer prognosis.”
💡 This demonstrates that the bacteria defendants’ product increases is not merely harmful but specifically linked to predicting cancer outcomes.
“Defendants market and label the Product as having the ability to ‘kill 99% of germs that cause bad breath, plaque & gingivitis’ and providing ‘a fresher and cleaner mouth than brushing alone.'”
💡 This shows defendants made affirmative health promises that directly contradict the concealed reality of bacterial proliferation.
“The Product that Plaintiff received was worthless because it has been shown to result in the proliferation of cancer-causing bacteria.”
💡 This establishes that a mouthwash causing cancer-bacteria proliferation has zero value, meaning consumers lost their entire purchase price.
“Defendants claim that ‘Listerine® antiseptic is the most extensively tested OTC mouthwash’ and that it had been ‘examined in more than 50 clinical trials more than 30 of which lasted 6 months or longer.’ Defendants further tout the ‘proven safety and tolerability of Listerine® in clinical studies’ and represents that ‘as powerful as LISTERINE® is, its safety is supported by fifteen 6-month studies conducted over a 20 year period in 3203 subjects.'”
💡 This proves defendants had extensive testing that should have revealed the bacterial proliferation, making their concealment intentional rather than ignorant.
“Upon information and belief, based on Defendants’ extensive testing of the safety and health consequences of the Product, Defendants are, or should reasonably have been aware of, the potential harmful effects of bacteria that proliferates with normal use of Listerine.”
💡 This establishes that defendants either knew or should have known about the cancer-bacteria risk from their own extensive testing programs.
“Defendants’ omission also violates 21 CFR § 201.80(e), which requires a manufacturer to revise its label ‘to include a warning as soon as there is reasonable evidence of an association of a serious hazard with a drug’, § 314.80(b) which places the responsibility for post-marketing surveillance on the manufacturer, and 73 Fed.Reg. 49605 which mandates that ‘manufacturers continue to have a responsibility under Federal law … to maintain their labeling and update the labeling with new safety information.'”
💡 This proves defendants violated multiple federal requirements to update labels when serious health hazards are discovered.
“Consumers lack the meaningful ability to test or independently ascertain or verify whether a product has dangerous side effects, especially at the point of sale, and therefore must and do rely on Defendants to truthfully and honestly report any health hazards associated with the Product on the Product’s packaging or labels.”
💡 This explains why label omissions are so harmful – consumers have no way to discover the danger themselves and must trust manufacturers.
“Defendants’ concealment was material and intentional because people are concerned with the health effects of products that they are putting onto and into their bodies. Indeed, consumers that use the Product do so to prevent oral disease and kill harmful bacteria, not to increase such harmful bacteria’s prevalence in their mouth.”
💡 This establishes that the concealment was calculated to maintain sales by hiding a fact that would have stopped consumers from purchasing.
“As set forth below, mouthwash products, such as Defendants’ Product, that cause the proliferation of cancer-causing bacteria are in no way safe for humans and are entirely worthless.”
💡 This frames the ultimate harm – consumers paid for a health product that is actually worthless because it increases cancer risk.
“The oral rinse/mouthwash market is a fast-growing, competitive, and lucrative industry, with market size that was valued at USD 6.51 billion in 2021 and is expected to expand at a compound annual growth rate of 7.1% from 2022 to 2030. The market is expected to reach USD 15.7 billion by 2022–2032.”
💡 This establishes the massive financial incentive defendants had to conceal cancer-bacteria risks that could damage market position.
“Additionally, these bacteria have been shown to survive longer than other bacteria under acidic conditions, like those found in the gut, which suggests that they may travel from the mouth to the gut through the digestive tract.”
💡 This proves the bacteria don’t just stay in the mouth but can travel through the body, creating cancer risks throughout the digestive system.
“These articles, when taken together, implicate F. nucleatum with every stage of colon cancer and show that this bacteria both increases as prognosis worsens exacerbating cancer progression through influence of the microenvironment.”
💡 This demonstrates the bacteria defendants’ product increases is not just associated with cancer but actively worsens cancer outcomes.
“If anything, Defendants’ labeling suggests the opposite. Defendants label the Product as having the ability to ‘kill 99% of germs that cause bad breath, plaque & gingivitis.’ Germs are a broad category of microscopic living things that can cause disease, including bacteria, viruses, fungi, and protozoa. Accordingly, by stating that the Product contains ingredients which will ‘kill 99% of germs’ associated with common oral ailments, a reasonable consumer would understand that it would eliminate most harmful bacteria in one’s mouth. Unfortunately for consumers, daily use of the Product, as recommended by Defendants, does the opposite—it has been shown to cause the proliferation of more bacteria associated with multiple deadly cancers.”
💡 This proves the marketing is not just incomplete but actively misleading, promising the opposite of what the product actually does.
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