A Look at a Recent Study on Chlorhexidine Mouthwash

As our understanding of the oral biome improves, it challenges us to reconsider oral care treatments and recommendations that are rooted in obsolete concepts of the oral environment.

This study, newly reported on, looked at a type of mouthwash developed under a previous understanding of the oral microbiome to understand how it interacts with the entire microbiome. The study found some unexpected results, and it’s worthwhile to take note of those findings and consider what they mean for oral health and what we still need to look at to continue developing our understanding of a healthy oral biome.

Your mouth, far from being a sterile environment, is home to numerous types of microorganisms—tiny little bacteria and fungi that live in your mouth and feed on the same foods that you take in. We have long suspected a link between oral bacteria and the development of oral caries.  Studies have found links between a particular form of strep bacteria and caries development, independent of sugary diets—a previous suspect in the theory of oral decay. Dental schools are teaching the importance of bacterial control for oral health. Given the association between caries and bacteria, it’s understandable why well-meaning people might try to kill all oral bacteria to control caries development. But, it turns out, according to this recent study, that using chlorhexidine-containing mouthwash to try and eliminate all bacteria may have unintended negative consequences.

Using a chlorhexidine mouthwash appears to have some problematic side effects. This study found that chlorhexidine mouthwash lowers the oral pH level of your mouth considerably. Without the bacteria that seem to help balance oral pH, a major factor that helps preserve oral health, your saliva loses it’s buffering capacity. That means it’s less able to return your mouth to a high pH level after eating and drinking, and it is less able to protect tooth enamel from dissolving in the acidic, low pH conditions. But, the chlorhexidine mouthwash itself is acidic, doubling down on the danger to your enamel.

Since your mouth does not stay sterile for long, bacteria will try to re-establish themselves quickly. Unfortunately, this study showed that acid-producing bacteria take over quickly after chlorhexidine mouthwash instead of the healthy biofilm bacteria that live in high pH, further increasing the acidic environment in the mouth and increasing the caries pressure on tooth enamel. Basically, it’s like spraying your garden with weed killer, only to find that you killed all the flowers but the weeds grew back and the flowers couldn’t because the soil had become unfavorable from the herbicide.

There’s good reason, based on current evidence, that chlorhexidine mouthwashes are not appropriate for everyone to use every day. But there are still times that your dentist may recommend you use an antimicrobial mouthwash. An antibacterial mouthwash prescribed by a dentist for short-term use to treat a specific infection has its place. Like all medicines, antimicrobial mouthwashes are not appropriate for everyone, every day. Just like the American Heart Association updated its guidelines about daily aspirin use because they re-evaluated the cost and benefits, it’s worth considering if indiscriminate use of OTC chlorhexidine mouthwash is more risky than beneficial. If you have a condition that would benefit from antimicrobial therapy, discuss with your dental care team which mouthwashes that can kill bacteria without lowering the oral pH and leaving your enamel susceptible to acid attack.

Another potentially worrisome side effect from chlorhexidine mouthwash confirmed by this study is that it changes how bacteria metabolized a waste product in the mouth. Healthy bacteria in the mouth turn nitrate into nitrite. While nitrate does not help us, nitrite reduces blood pressure. The study found that while patients used chlorhexidine mouthwash, their nitrite levels may be lowered and blood pressure higher.

So, what’s the takeaway?

If you are hesitant to remove mouthwash from your daily routine for any reason, consider swapping out a potentially acidic mouthwash for a pH balanced mouthwash with ingredients that benefit oral health. A high pH mouthwash with xylitol might actually provide the benefits to your oral health you were looking for from chlorhexidine mouthwash without the risk of higher blood pressure. If your dentist recommends antimicrobial therapy to treat a specific condition, look for a treatment rinse that provides a high pH, healthy environment to aid your saliva in keeping your enamel safe while you eliminate infectious bacteria.





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