Twice a Day, Every Day: Toothpaste Preservatives and Your Oral Microbiome
Brush twice a day and you expose your mouth to the same product about 730 times a year. Most people read the front of the tube and skip the back. On the back, near the end of the ingredient list, is usually a preservative: a chemical added because it stops microbes from growing.
Your mouth is also home to microbes, and most of them are on your side. So it is fair to ask whether an ingredient designed to stop microbial growth affects the community you want to keep. The honest answer is that science has only begun to study this. Here is what the research shows so far, and where it stops.
Your mouth is an ecosystem, not a surface to sterilize
The Human Oral Microbiome Database currently lists 557 bacterial taxa that live in the human mouth. Nearly a quarter of them have never been grown in a lab. Researchers have come to see most of these bacteria as residents that help keep the mouth healthy, not as germs to wipe out.
One example is the nitrate pathway. Certain bacteria on the tongue convert nitrate from vegetables into nitrite. Your body then turns nitrite into nitric oxide, a molecule involved in regulating blood pressure.
We know this pathway can be disrupted. In a 2020 University of Plymouth study, seven days of chlorhexidine mouthwash reduced oral microbial diversity. It increased acid-associated bacteria, lowered saliva pH and reduced nitrite in saliva and blood. Chlorhexidine is a strong antiseptic, not a toothpaste preservative. But it shows that a twice-daily antimicrobial rinse can reshape the oral community within a week.
Why toothpaste needs preservatives in the first place
Toothpaste contains water. It also sits in a warm bathroom and gets opened with a wet brush for months. Without a preservative, bacteria and mold could grow in the tube. So preservatives serve a real safety purpose.
The most common ones are parabens (methylparaben, propylparaben) and sodium benzoate. A 2016 survey from Korea's Gyeonggi Province Institute of Health and Environment tested 75 toothpastes and mouthwashes. It found preservatives in 37 of them, all within legal limits:
| Preservative | Products containing it | Concentration found |
|---|---|---|
| Methylparaben | 26 | 0.003–0.19% |
| Sodium benzoate | 14 | 0.1–0.3% |
| Propylparaben | 11 | 0.002–0.02% |
One detail stands out. Among the children's toothpastes, eight were labeled "paraben-free." Five of those still contained sodium benzoate. "Paraben-free" does not mean "preservative-free."
What the research shows, ingredient by ingredient
The short version: parabens have the most evidence of an association with a shifted oral microbiome. Sodium benzoate and triclosan have less.
| Ingredient | Study | Design | Finding |
|---|---|---|---|
| Parabens | Vindenes et al., Frontiers in Microbiology, 2022 | 477 Norwegian adults; urine paraben levels vs. gum-line bacteria | Highest propylparaben levels linked to lower abundance of 7 bacterial genera, mostly normal residents |
| Parabens, sodium benzoate | Kim et al., Archives of Oral Biology, 2025 | Lab tests on salivary enzymes | Parabens reduced peroxidase activity; both inhibited lysozyme in solution |
| Sodium benzoate | Østergaard, Acta Odontologica Scandinavica, 1994 | Lab tests on 115 plaque bacteria strains, plus saliva after brushing | Did not inhibit streptococci; levels in saliva fell sharply within 30 minutes |
| Triclosan | Poole et al., mSphere, 2016 | Randomized crossover, 4 months with and 4 months without | No significant change in oral or gut microbiome composition |
Parabens
Parabens work mainly against fungi and Gram-positive bacteria. The longer the paraben's chemical chain, the stronger it is. Butylparaben is the strongest, followed by propyl-, ethyl- and methylparaben.
In the Norwegian study, people with the highest propylparaben levels had less of several bacterial groups at the gum line. Those with any detectable butylparaben had less of 16 different genera. The authors noted most of the affected bacteria were commensals, meaning normal residents of a healthy mouth.
The same study linked product use to exposure. People who used mouthwash twice a day had a median urine methylparaben level of 67.8 ng/mL, versus 14.6 ng/mL in people who used it less than weekly.
Parabens also appear to affect saliva itself. Saliva contains enzymes like lysozyme and peroxidase that help control bacteria naturally. The 2025 lab study found parabens lowered peroxidase activity. Its authors recommended sodium benzoate over parabens for oral care products.
Sodium benzoate
Sodium benzoate looks milder on oral bacteria. In the 1994 study, it did not stop the growth of any streptococci at the concentrations tested. It did inhibit some gum-disease bacteria, but only at high concentrations. After brushing, its level in saliva dropped rapidly within 30 minutes. That study used a toothpaste with 10% sodium benzoate, far more than the 0.1–0.3% found in the Korean survey.
Triclosan
Triclosan is an antibacterial, not a preservative, but it was once common in toothpaste. In a double-blind crossover trial, people used personal care products with and without it for four months each. Researchers found no difference in oral or gut microbiome composition. The authors noted their sample was small.
What the evidence does not show yet
We could not find a published trial that isolates the effect of toothpaste preservatives on the oral microbiome. Keep these limits in mind:
- Association, not cause. The Norwegian paraben study measured parabens in urine, which reflects exposure from cosmetics, food and packaging, not toothpaste alone. It shows a link, not proof that parabens caused the shift.
- Toothpaste frequency alone showed no link. In the same study, how often people brushed with fluoride toothpaste was not associated with oral bacterial diversity. Frequent mouthwash use was.
- Lab results are not the mouth. Enzyme and bacterial-growth tests happen in test tubes. Saliva, food and brushing change conditions in real life.
- Unknown health impact. Even the chlorhexidine researchers said more work is needed to know whether lower diversity itself raises disease risk.
The fair summary: preservatives are antimicrobial by design, some are linked to measurable shifts in oral bacteria, and the long-term effect of twice-daily exposure has not been studied directly.
What you can do
Keep brushing twice a day. The benefits of brushing are well established; the open question is only about some of the ingredients. A few practical steps:
- Read the full ingredient list. Preservatives usually appear near the end as methylparaben, propylparaben, sodium benzoate or potassium sorbate.
- Don't stop at "paraben-free." As the Korean survey showed, paraben-free products often use a different preservative instead.
- Think about your mouthwash too. In the Norwegian study, twice-daily mouthwash use was linked to both higher paraben exposure and lower bacterial diversity. Strong antiseptic rinses like chlorhexidine are meant for short-term use your dentist recommends.
- Consider water-free formats. Preservatives exist because water lets microbes grow. Dry formats like toothpaste tablets and tooth powders contain little water, so they can be formulated without a preservative system. Check the label to confirm.
Where NovaTabz stands
NovaTabz toothpaste tablets contain no preservatives. No parabens, no sodium benzoate, no potassium sorbate. Because each tablet is dry, there is no water in the product for microbes to grow in, so it doesn't need them.
If you'd rather skip the preservative question entirely, that's one less ingredient to think about twice a day.
Sources
- Vindenes HK et al. Exposure to Antibacterial Chemicals Is Associated With Altered Composition of Oral Microbiome. Frontiers in Microbiology, 2022
- Kim MJ et al. Effects of preservatives on the activities of salivary enzymes. Archives of Oral Biology, 2025
- Østergaard E. Evaluation of the antimicrobial effects of sodium benzoate and dichlorobenzyl alcohol against dental plaque microorganisms. Acta Odontologica Scandinavica, 1994
- Poole AC et al. Crossover Control Study of the Effect of Personal Care Products Containing Triclosan on the Microbiome. mSphere, 2016
- Lee SB et al. Monitoring of Antimicrobial and Preservatives in Dentifrice, 2016
- University of Plymouth. Study shows commonly used mouthwash could make saliva significantly more acidic, 2020
- Human Oral Microbiome Database (eHOMD)
Disclaimer: The information provided in this article is for educational and informational purposes only and is not intended as professional medical or dental advice, diagnosis, or treatment. Always seek the advice of your dentist, physician, or other qualified health provider with any questions you may have regarding a medical or dental condition.