Mouthwashes are a common addition to daily oral hygiene routines, often used to achieve fresher breath and a cleaner mouth. The widespread use of these products raises concerns about disrupting the delicate ecosystem of the mouth, known as the oral microbiome. This complex community of microorganisms exists in a balanced state important for overall health. The central question is whether the non-selective killing action of mouthwash removes beneficial bacteria alongside the harmful ones.
Understanding the Oral Microbiome
The oral cavity is not a sterile environment; instead, it hosts a diverse and constantly interacting community of microbes that play a significant role in health. These commensal, or “good,” bacteria are involved in maintaining a stable oral environment, helping to prevent the overgrowth of pathogenic species that can cause disease. A balanced oral microbiome is considered a state of health, where beneficial and potentially harmful microbes coexist without leading to illness.
Certain species of commensal bacteria, such as Neisseria and Rothia, are important because of their metabolic function. These microbes possess enzymes that reduce inorganic nitrate, consumed primarily through the diet in vegetables, into nitrite. This process is the first step in a larger physiological pathway important for systemic health. The presence of these nitrate-reducing bacteria is a marker of a functional and healthy oral ecosystem.
The Mechanism: How Mouthwash Ingredients Affect Bacteria
Antiseptic mouthwashes are formulated to destroy microbes, and they achieve this using ingredients that are typically non-selective in their action. Common active ingredients include chlorhexidine (CHX), cetylpyridinium chloride (CPC), and essential oils. These compounds are broad-spectrum antimicrobials, meaning they kill a wide variety of microorganisms without distinguishing between beneficial and disease-causing ones.
Chlorhexidine is a cationic compound that works by binding to the negatively charged cell membranes of bacteria. This binding disrupts the structural integrity of the cell wall, causing the contents to leak out and resulting in cell death. Similarly, cetylpyridinium chloride acts on microbial proteins and lipids, causing cellular leakage and rapid death. Essential oils, such as thymol and eucalyptol, penetrate the bacterial cell membrane, altering its function.
Systemic Consequences of Microbiome Disruption
The killing of beneficial bacteria by antiseptic mouthwash has consequences that reach far beyond the mouth, primarily through the disruption of the nitrate-nitrite-nitric oxide pathway. Dietary nitrate from foods like leafy greens and beets is first converted to nitrite by oral bacteria, which is then swallowed. Once in the stomach and bloodstream, this nitrite is further converted into nitric oxide (NO).
Nitric oxide is a signaling molecule and vasodilator, meaning it helps relax and widen blood vessels. This vasodilation is essential for regulating blood pressure and maintaining proper cardiovascular function. When antiseptic mouthwash reduces nitrate-reducing bacteria, the conversion of nitrate to nitrite is impaired, leading to less bioavailable nitric oxide. Studies show mouthwash use can reduce oral nitrite production by up to 90% and plasma nitrite levels by about 25%.
This reduction in nitric oxide availability has been associated with a sustained increase in both systolic and diastolic blood pressure. Some research indicates that people who use mouthwash twice or more daily may have a significantly higher risk of being diagnosed with hypertension. Furthermore, the resulting oral dysbiosis, or microbial imbalance, is an area of emerging research that suggests a potential link between oral health and cardiometabolic issues, including insulin resistance.
Selecting and Using Mouthwash Wisely
For individuals who choose to incorporate a mouthwash into their routine, understanding the product type is helpful. Cosmetic mouthwashes primarily offer temporary breath freshening and do not contain active ingredients that significantly combat plaque or gingivitis. Therapeutic mouthwashes, on the other hand, contain antimicrobial agents or fluoride designed to address specific oral health concerns.
If a therapeutic, antiseptic mouthwash is recommended, it should be reserved for short-term use and guided by a dental professional, such as following surgery or during acute gum inflammation. For daily use, non-antiseptic or alcohol-free formulations are preferable to minimize disruption to the oral microbiome. Alcohol-free options also reduce the risk of drying out the mouth, which negatively affects the natural cleansing action of saliva.
When using a fluoride-containing mouthwash for cavity prevention, it is recommended to avoid rinsing immediately after brushing. This practice ensures that the fluoride from the toothpaste remains on the tooth surface for a longer period, maximizing its protective effect. For any mouthwash, following the directions for swishing time and avoiding rinsing, eating, or drinking for at least 30 minutes afterward helps the active ingredients work most effectively.