What’s the deal with the "Listerine mouthwash causes cancer" claim?

It is sobering when everyday items we trustingly pick off racks at the supermarket turn out to be a health hazard. Most consumers still hesitate before buying Maggi noodles because of the excessive quantities of lead that were reported in them back in 2015. Now, researchers have foisted some serious allegations on Listerine mouthwash — a household item worldwide — saying that its regular use can cause cancer.

But how seriously should you take these claims?

In 1879, a St. Louis-based doctor named his germicidal concoction of essential oils after Joseph Lister. Before Listerine went on to become the #1 dentist-recommended mouthwash brand, it started out as a humble disinfectant, cleaning agent, cure for dandruff, hair tonic, deodorant, and even a "beneficial remedy" for various bacterial and viral diseases. But hey, who doesn’t have a bit of an identity crisis in their early days?

It didn’t take long for a marketing dude to recognise its potential as an oral antiseptic and popularise it. While it did take time to catch on, Listerine turned out to be a huge hit among people — nobody wanted stinky breath, after all. The mouthwash has had quite a journey since its discovery over 130 years ago. But its premise remains the same — germ removal.

Many of us have cultivated the habit of using the mouthwash for a quick rinse. This is probably why all the recent headlines this week linking Listerine to cancer had our eyes widening in horror. However, the narrative seems to have been twisted a tad bit. So before you yeet your mouthwash in the trash can, you might want to understand the context behind what the researchers have really said.
A crucial link
Scientists in Germany were trying to determine if mouthwash use could impact the incidence of STIs in gay men. The 59 participants used Listerine Cool Mint mouthwash every day for three months and another three months of a placebo rinse.

In the case of Listerine, the researchers found high concentrations of two species of bacteria in their mouths at the end of the three-month period — Fusobacterium nucleatum and Streptococcus anginosus. Both of these bacterial species have previously been linked to cancers like oral and colorectal.

The study, published in the Journal of Medical Microbiology, stated that “Listerine use was associated with an increased abundance of common oral opportunistic bacteria previously reported to be enriched in periodontal diseases, oesophageal and colorectal cancer and systemic diseases”.
Listerine may not directly cause bacterial proliferation
Some might argue that the ethanol in Listerine was triggering this surge in bacterial counts since there are pre-existing links between these bacterial species and alcohol consumption. In fact, Professor Kenyon, who worked on the study, suggested that if you did want to use a mouthwash, an alcohol-free kind might be a better option.

You might be wondering how this is possible since alcohol is associated with killing germs — that should’ve been the whole point of adding ethanol to the blend, wasn’t it? However, Listerine is only around 20% alcohol, which isn’t nearly enough to destroy all the bacteria in your mouth. It is, instead, likely used as a preservative and carrier for the other active ingredients in the mouthwash, as per sources.

But the alcohol content can cause dehydration and the lack of beneficial salivary enzymes could sometimes shift the power dynamics in favour of the cancer-causing villains like Fusobacterium nucleatum and Streptococcus anginosus.
What Listerine had to say about the whole ordeal
The study says, “Listerine use was associated with an increased abundance of common oral opportunistic bacteria”. However, the authors add that “the findings suggest that the regular use of Listerine mouthwash should be carefully considered”. This implies that the study’s findings are not conclusive and may need further scrutiny to establish a clear link.

A spokesperson for the company that owns the Listerine brand, told the Daily Mail that “Based on our initial review, the published trial lacks several important design controls and adequate rigour to make any conclusions about the potential impact on human health.”

Plausible correlation due to other factors such as dietary habits, smoking, alcohol consumption or already poor hygiene — all of which are also linked to oral cancer — have not properly been accounted for in the study. The sample size is also pretty small and doesn’t necessarily represent an entire population. As pointed out by the brand itself, some participants could have used mouthwash after the development of oral cancer. However, this potential reverse causation has also not been acknowledged in the study.

While we strongly advise getting your primary healthcare provider’s opinion on whether or not you should include Listerine in your oral care routine, we do think it is too early to label the mouthwash a harbinger of cancer.

This link between alcohol-based mouthwashes and cancer is not without merit, but more research is needed to establish a stronger association between the two. In the meantime, if you do feel some sense of loyalty towards Listerine but want to go the alcohol-free mouthwash route, the brand does already have zero alcohol options.