Can mouthwash cure gonorrhea? That’s the claim that Listerine made way back in 1879.
With the incidence of gonorrhea in men who have sex with men on the rise, researchers in Melbourne, Australia, set out to test Listerine’s claim.
The group started out by testing how effectively two Listerine products killed Neisseria gonorrhoeae (the bacterium that causes gonorrhea), compared to phosphate buffered saline. Both mouthwashes, Cool Mint and Total Care, contain 21.6% alcohol. Treating the cells with a 1:2 or 1:4 dilution of either mouthwash reduced the colony forming units from > 10^5 to < 10^2.
With promising in vitro results, they moved on and conducted a randomized, controlled trial. The study included 196 men - 58 were culture positive for the bacteria at the posterior oropharynx and/or the tonsillar fossae before the study.
Of those 58, 33 were placed in the Listerine group, and 25 were placed in the saline group. In the saline group, 84% remained positive for N. gonorrhoeae 5 minutes after rinsing and gargling with saline for 1 minute, while only 52% of the Listerine group tested positive. The researchers admit that their study had limitations - future studies will test daily use of mouthwash, for example.
The big question, however, is this - can oral N. gonorrhoeae be transmitted to the urethra or other body sites? The urethra, for example, is a site at which infection can cause infertility or sterility. Indeed, the authors reference a set of studies concluding that N. gonorrhoeae can be transmitted from the mouth and throat to other body sites, producing a symptomatic infection.
These findings could actually make a big impact on public health. Mouthwash is cheap, readily available, and easy to use. According to study author Eric Chow, “use of mouthwash could reduce the duration of infection and hence could reduce the number of gonorrhoea cases. If the number of gonorrhoea cases [reduces], it will minimize the use of antibiotics.”
Gonorrhea aside, Listerine has a pretty interesting history. The product was named after Joseph Lister who subscribed to Louis Pasteur’s theory that microbes caused infection. (The bacterial genus Listeria is also named after Lister.) In 1865, Lister showed that sterilizing surgical tools and dressings with carbolic acid reduced the incidence of infection. Not long after, in the late 1800s, Joseph Lawrence developed Listerine - a surgical antiseptic containing alcohol, eucalyptol, menthol, and methyl salicylate, among other ingredients. By 1914, it was the first mouthwash to be sold over the counter in the US. Gargle on!