No, Listerine doesn’t work as a mosquito repellent

Listerine is formulated to kill the germs in your mouth. Could it also keep summer pests off your skin?

A viral Facebook post claims that it works. Titled "How to Kill Mosquitoes - NOT A JOKE," the author of the message says they were at a party where guests were being plagued by mosquitoes until a man sprayed Listerine mouthwash around the immediate area, seemingly repelling the pests.

"The next year I filled a four-ounce spray bottle and used it around my seat whenever I saw mosquitoes," the post claims. "And voila! That worked as well ... during the summer, I don't leave home without it."

One version of the post, shared more than 9,000 times, was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)

Claims about Listerine's ability to fight more than just plaque and gingivitis have persisted for nearly two decades, seemingly first appearing in chain emails from the early 2000s.

The primary belief behind these claims is that the essential oils used in the mouthwash act as natural bug repellents, according to The New York Times. The oils contained in Listerine — which the brand says are used for their "disinfecting abilities and antimicrobial qualities" — are derived from thyme, eucalyptus, mint and wintergreen plants.

While most repellents use synthetic compounds like DEET or picaridin as active ingredients to ward off mosquitoes, the Centers for Disease Control and Prevention identified a refined form of lemon eucalyptus oil as being safe and effective in plant-based repellents.

The agency doesn't recommend using pure lemon eucalyptus oil as a repellent.

"It has not undergone similar, validated testing for safety and efficacy and is not registered with EPA as an insect repellent," the CDC said. 

A study conducted by the London School of Hygiene and Tropical Medicine in the 1990s found that eucalyptus-based insect repellent did provide protection against mosquitos on par with repellents containing DEET. However, the eucalyptus-based repellents used in the study contained a 50% concentration of the oil.

Listerine contains concentrations of less than 1% of the essential oils.

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The CDC reports that a bug repellent must have at least 10% of the active ingredient to offer even a limited amount of protection against mosquitos. Even then, that protection would last only one or two hours.

Commercial products like Repel's plant-based lemon eucalyptus insect repellent contain around 30% of the oil. Another plant-based repellent, Off! Botanicals, uses a 10% concentration of a synthetic version of the active ingredient. 

We tried to contact Johnson & Johnson, the producer of Listerine, about the claims, but didn’t get a response.

A Facebook post claimed Listerine was an effective mosquito repellent. Similar claims point to the essential oils contained in Listerine as the source of its bug-fighting powers.

While the CDC considers oil of lemon eucalyptus an effective repellent, it found that the concentration of the oil must be at least 10% in order to provide even limited protection. The concentrations of the oils used in Listerine are less than 1%.

We can’t say the scenario described at the party never happened. But we can say that science doesn’t approve this method to keep mosquitoes away. We rate this claim Mostly False.