Does Mouthwash Reduce Risk of Oral STDs?

Close up of toothbrush and mouthwash
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Although many people aren't aware of the risk, a number of STDs can be spread through oral sex. Gonorrhea, chlamydia, syphilis, HPV, and herpes can all be spread through fellatio and cunnilingus. The most effective way to reduce the overall risk of oral STD transmission is screening, treatment, and using barriers for oral sex. However, recent studies have also begun to suggest that using antiseptic mouthwash, such as Listerine, may also be able to reduce the risk of some oral STD transmission.

Note: It is theoretically possible to get HIV through oral sex. However, transmission through oral sex is thought to be quite rare. The risk of transmission of other STDs is much higher.

Can Mouthwash Help With Oral STDs?

There is a growing body of literature suggesting that mouthwash may play a role in reducing the risk of oral STDs. A 2017 study published in the journal Sexually Transmitted Infections looked at whether gargling with Listerine could be an effective way to reduce the risk of oral transmission of gonorrhea. Oral gonorrhea is a growing concern, in part because of the growing number of antibiotic resistant cases.

What the study found was that after gargling for one minute, the men were half as likely to have living bacteria in their mouth. (This was measured by the studies ability to culture bacteria from mouth swabs. Before the gargle, all men were positive for live bacteria.) This was a much greater reduction than for men who gargled with salt water. There was only a 16 percent reduction in the number of those men with living bacteria on their mouth swabs.

On the other hand, follow up studies did not find that mouthwash use was significantly associated with actual gonorrhea transmission. One study saw an increase in mouthwash use with age, and a decrease in oral gonorrhea, but the correlation was not statistically significant. Another study found no protective effect for men who used mouthwash regularly. They got oral gonorrhea just as often as men who did not. 

That doesn't mean mouthwash is useless. But it does point out that it's important to treat results with caution. An example of this is a 2005 study of how a 30 second rinse with Listerine affected people with herpes also found positive results. They saw a significant reduction in active herpes virus for more than 30 minutes after mouthwash use. The effect had worn off by 60 minutes, but the researchers still saw a strong benefit in that time period. In other words, the mouthwash helped right after people used it, but not necessarily long term. 

Basic Research on Mouthwash and STDs

Unfortunately, there have not been too many studies looking at the effects of mouthwashes on STDs in the human body. However, several studies have examined the effects of such mouthwashes in vitroIn such studies, both Listerine and chlorhexidine based mouthwashes have been shown to limit the growth of both HIV and herpes viruses. Those results can't be directly extrapolated to how the mouthwashes work in people, but it definitely makes research on the role of mouthwash in oral STD prevention something that scientists are likely to continue working on in the future.

It's worth mentioning that research has also examined the role of oral hygiene in limiting oral HPV infection. A large study published in 2013 in Cancer Prevention and Research found that poor oral health was associated with oral HPV infection. That study didn't look directly at the impact of mouthwash use on HPV infection. They did find an increased risk of HPV in people who used mouthwash for treating oral symptoms. However, that association was more likely to be about the fact that oral symptoms requiring mouthwash are associated with poor oral health.

Some people may just be wondering if Listerine is simply a magic bullet that kills all bacteria and viruses. The answer seems to be no. Looking at the data on Listerine and STDs, the success stories aren't because Listerine is equally effective against all pathogens. It does seem to good job of reducing the amount of certain infections, but that effect isn't universal. Other pathogens, like rotavirus and adenovirus, are not as efficiently killed off by gargling.

A Word From Verywell

Right now, the best way to prevent the spread of oral STDs is to consistently use barriers for oral sex.

However, that isn't always a practical option. When it's not, gargling with an antiseptic mouthwash such as Listerine before sex may reduce your risk of transmitting any oral STD to your partner. (It's theoretically possible that gargling after sex might reduce your risk of catching such an STD. However, it's very hard to do that research ethically. As such, there isn't any clear data.)

Is gargling with mouthwash as good as using oral sex barriers for preventing the spread of oral STDs? Absolutely not. However, it looks like, for at least some STDs, it is definitely better than doing nothing. 

Sometimes STD prevention is about what's possible, not what's best. When talking about sexual risk and behavior. It's really important not to let the perfect be the enemy of the good. There are many people who aren't willing to use barriers for oral sex but are happy enough to gargle. It may not be clear how much mouthwash helps, but it's certainly better than doing nothing at all. 

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