Mouthwash is a liquid oral hygiene product designed to freshen breath and kill bacteria in the mouth. Most mouthwashes contain antibacterial ingredients like cetylpyridinium chloride, essential oils, hydrogen peroxide, chlorhexidine, or zinc chloride. These ingredients disrupt bacterial cell walls or metabolism, effectively killing many oral bacteria. However, the question remains if using mouthwash eliminates all bacteria in the mouth.
How Mouthwash Kills Bacteria
Most mouthwashes work by killing bacteria through the following mechanisms:
Disrupting cell membranes
Ingredients like chlorhexidine and cetylpyridinium chloride are positively charged molecules called cationic surfactants. When these ingredients come into contact with negatively charged bacteria, they disrupt the bacterial cell membrane, effectively killing the cell.
Denaturing proteins
Ethanol and hydrogen peroxide contain reactive oxygen species that can damage bacterial proteins and enzymes through oxidation. This damages essential bacterial components, leading to cell death.
Disrupting metabolism
Essential oils like thymol, eucalyptol, and menthol found in mouthwashes can permeate bacterial cell membranes. Once inside the cell, these oils can disrupt enzymatic reactions and interfere with the electron transport chain, inhibiting metabolism and killing bacteria.
So in summary, mouthwashes use multiple mechanisms focused on damaging bacterial structures and processes to efficiently kill oral microbes. But do they eliminate 100% of all bacteria with regular use?
Does Mouthwash Eliminate All Oral Bacteria?
While mouthwashes can reduce bacterial load, no mouthwash can completely sterilize the mouth. Here are some key reasons why:
Bacteria can form biofilms
Many oral bacteria grow in sticky biofilms on surfaces like teeth, gums, cheeks, and tongue. Bacteria deep within these biofilms are protected from mouthwash exposure and are not effectively killed.
Bacteria can reside in inaccessible areas
The oral cavity has many nooks and crannies where mouthwash cannot easily penetrate to reach bacteria, like in dental plaque, gum pockets, fissures on the tongue, etc. Bacteria in these areas often survive mouthwash use.
Some bacteria are resistant
A small subset of oral bacteria have inherent or acquired resistance to ingredients found in mouthwashes. For example, some strains of Streptococcus mutans can produce polymers that protect against cationic surfactants like chlorhexidine.
Mouthwash washes away but does not adhere
Mouthwashes briefly pass through the mouth to kill bacteria but do not stick around long enough to have sustained antimicrobial action. Many bacteria can therefore repopulate areas of the mouth soon after mouthwash use.
Saliva dilutes mouthwash
Saliva contains enzymes like esterases that start breaking down mouthwash ingredients like essential oils. Saliva also dilutes the concentration of the mouthwash, making it less effective at killing bacteria the longer it is in the mouth after rinsing.
Mouthwashes cannot access all areas
There are over 700 species of bacteria that inhabit the oral microbiome. Many reside in intricate structures like the deep crevices on the tongue or microscopic gaps between teeth that are impossible for mouthwash to access and sanitize.
So while mouthwash has broad-spectrum antimicrobial activity, current formulations cannot fully eliminate the diverse bacterial landscape in the oral cavity.
How Much Bacteria Does Mouthwash Kill?
While mouthwash does not sterilize the mouth completely, it still provides a significant temporary decrease in bacterial load. Some key statistics on mouthwash effectiveness include:
- Mouthwash can result in a 6-99% reduction in oral bacteria immediately after use.
- Chlorhexidine mouthwash typically reduces bacterial load by ~50-80% when used as recommended.
- Essential oil mouthwashes like Listerine can decrease bacteria by ~50% within 30 seconds of use.
- In gingivitis patients, using antimicrobial mouthwash twice daily can lower oral bacteria by 45-65%.
- Hydrogen peroxide mouthwashes may reduce oral bacteria by 43-91% depending on concentration.
So while mouthwash cannot kill 100% of all oral bacteria, it can temporarily reduce bacterial numbers by about 50-90% on average. But this reduction is transient as bacteria regrow and repopulate the mouth within hours.
Which Oral Bacteria Are Most Affected by Mouthwash?
Mouthwashes tend to be broad spectrum, killing both gram-positive and gram-negative oral bacteria. However, some specific types of bacteria are more susceptible to mouthwashes than others.
Gram-positive cocci
Gram-positive bacteria have a thick peptidoglycan cell wall but lack an outer membrane. Mouthwash ingredients like chlorhexidine and essential oils easily penetrate and damage the cell wall of gram-positive cocci like Streptococcus and Staphylococcus species.
Gram-negative rods
Gram-negative bacteria have an outer membrane that provides some protection. But mouthwashes like those containing cetylpyridinium chloride can disrupt this outer membrane and be highly effective against many gram-negative rod species.
Anaerobes
Many oral anaerobes like Porphyromonas and Prevotella species are extremely susceptible to oxygenating ingredients in mouthwashes like hydrogen peroxide, which damages their cell components.
Free floating planktonic bacteria
Bacteria floating in saliva are directly exposed to the mouthwash and easily killed. Bacteria within biofilms or shielded by tooth and gum crevices tend to be more resistant.
So in general, gram-positive cocci, gram-negative rods, anaerobes, and unattached planktonic bacteria are most susceptible to killing by mouthwash.
Are Certain Bacteria Resistant to Mouthwash?
While many oral bacteria are susceptible to mouthwash, some specific types display greater resistance:
Streptococcus mutans
Streptococcus mutans can produce a glucan polymer biofilm matrix that protects the cells against antimicrobials like chlorhexidine.
Enterococcus faecalis
Some studies have found the common oral commensal E. faecalis persists after use of mouthwashes containing chlorhexidine and essential oils.
Porphyromonas gingivalis
This keystone pathogen associated with periodontitis can develop resistance to triclosan and other antiseptics with prolonged exposure.
Fusobacterium nucleatum
F. nucleatum is a core species in oral biofilms and its position within the biofilm appears to provide some protection against mouthwash.
Aggregatibacter actinomycetemcomitans
This gram-negative species linked to aggressive periodontitis is intrinsically less susceptible to cationic antiseptics like chlorhexidine.
So bacteria that reside in biofilms, have outer membrane barriers, or utilize antimicrobial resistance mechanisms tend to be most resistant to the effects of mouthwash.
Does Mouthwash Disrupt the Oral Microbiome?
The oral microbiome is comprised of over 700 diverse bacterial species that inhabit the mouth. While mouthwashes reduce bacterial load, they can also cause unintended disruption of the natural microbiome:
- Most mouthwashes cannot selectively eliminate only pathogenic bacteria.
- Indiscriminate killing affects both commensal and harmful bacteria.
- This can allow pathogens like Candida albicans to overgrow after use.
- Chlorhexidine appears to have prolonged microbiome disruption compared to essential oil rinses.
- Mouthwash use alters bacterial community structure and delays reestablishment.
- Microbiome shifts may impact colonization resistance against pathogens.
So while mouthwashes provide short-term decreases in bacterial load, frequent or improper use could come with the tradeoff of disrupting the natural oral microbiome. This highlights the importance of using mouthwash as an adjunct, not as a replacement, for mechanical oral hygiene habits like brushing and flossing.
Comparison of Mouthwash Ingredients
Mouthwashes contain different antibacterial ingredients with varying spectrums of activity:
| Ingredient | Examples | Mechanism | Bacteria Killed |
|---|---|---|---|
| Chlorhexidine | Peridex | Disrupts cell membrane | Broad spectrum – gram positive and negative |
| Cetylpyridinium chloride | Scope, Crest | Disrupts cell membrane | Broad spectrum – gram positive and negative |
| Hydrogen peroxide | Peroxyl | Oxidative damage | Anaerobes, gram-negative rods |
| Essential oils | Listerine | Disrupts metabolism | Broad spectrum – gram positive and negative |
| Alcohols | Generic brands | Protein denaturation | Broad spectrum – gram positive and negative |
This table summarizes the main antimicrobial ingredients found in various mouthwash brands and their bacterial targets. Overall, chlorhexidine and essential oil mouthwashes tend to have the broadest spectrum of antibacterial activity against oral microbes.
Should You Use Mouthwash?
Despite not eliminating all oral bacteria, there are some benefits to using mouthwash:
Freshens breath
Mouthwashes contain flavorants like mint along with antibacterials to leave breath fresh.
Reduces gum inflammation
Using antimicrobial mouthwashes helps control bacteria-induced gingivitis and bleeding.
Helps manage periodontal diseases
Adjunct use of antimicrobial mouthwashes aids in managing periodontitis.
Lowers caries risk
Mouthwashes with fluoride help remineralize enamel and reduce cavities.
Helps clean hard-to-reach areas
Mouthwash can access small spaces between teeth and dental appliances.
May improve oral cancer outcomes
Some data indicates mouthwash may help reduce oral cancer recurrence after surgery.
So while mouthwash cannot completely remove all oral bacteria, its antimicrobial effects provide various oral health benefits when used properly alongside regular brushing and flossing.
How to Use Mouthwash Appropriately
To gain the most oral health benefits from mouthwash without disrupting the oral microbiome, consider these tips:
- Use mouthwash as an adjunct, not as a replacement, for mechanical cleaning.
- Choose an ADA-approved antimicrobial mouthwash with broad activity against pathogens.
- Swish the mouthwash vigorously for 30-60 seconds to penetrate all areas.
- Aim to use mouthwash just 1-2 times daily at most.
- Rinse with water after to wash away excess mouthwash.
- Spit out mouthwash – do not swallow.
- Wait at least 30 minutes to eat or drink after use.
- See your dentist regularly to check for signs of oral disease.
Following these best practices allows you to incorporate mouthwash into your oral care routine in a healthy way without overusing it.
Conclusion
While mouthwashes are very effective at killing oral bacteria, no existing formulation can completely eliminate all bacteria from the intricate and diverse microbial communities residing in the mouth. Mouthwashes reduce bacterial load transiently but oral bacteria quickly rebound and recolonize all areas of the mouth. Frequent overuse of mouthwash could come at the detriment of disrupting the natural oral microbiome. Therefore, it is best to use mouthwash in moderation as a supplement to regular mechanical brushing and flossing for a healthy oral care regimen.