Probiotic toothpastes and mouthrinses mostly fail basic probiotic tests

Walk down the oral care aisle of any well-stocked pharmacy and you will now find toothpastes and mouthwashes branded with the word probiotic, promising to seed your mouth with beneficial bacteria rather than blast it with antimicrobials. A rigorous new laboratory audit suggests that most of these products do not deliver on that promise. When researchers in Belgium bought 16 probiotic toothpastes and 6 probiotic mouthrinses from European and American markets and subjected them to a battery of microbiological tests, only two toothpastes contained culturable bacteria that matched the probiotic species declared on their labels. Not a single mouthrinse passed that basic test.

The study, led by Mehraveh Saghi and Wim Teughels of KU Leuven together with colleagues at Ghent University, was published in Frontiers in Oral Health. Its central question is deceptively simple: do these products actually contain live microorganisms? By the internationally accepted definition, a probiotic is a live microorganism that, when administered in adequate amounts, confers a health benefit on the host. That definition contains three testable conditions, and the team checked all of them. They asked whether the bacteria were present, whether they were alive, whether they could grow and form colonies, and whether the species on the label matched the species in the tube.

The technical approach combined classical microbiology with molecular tools. Each product was plated onto selective and non-selective agar media, including de Man, Rogosa and Sharpe agar favored by lactobacilli, Luria-Bertani agar for Bacillus species, and blood agar to flag potential contaminants. Colonies were counted as colony-forming units, and the identity of the isolates was confirmed by Sanger sequencing of the 16S rRNA gene. In parallel, the researchers used quantitative PCR to measure total bacterial DNA, and a refinement called viability qPCR, in which the dye PMAxx binds DNA from dead or membrane-compromised cells and blocks its amplification, allowing live cells to be counted separately from dead ones. Finally, deep 16S rRNA amplicon sequencing, processed with the DADA2 pipeline and the SILVA database, revealed the full bacterial species composition of each product.

The results were striking. Twenty of the 22 products contained no viable, culturable bacteria consistent with their probiotic claims. Eight formulations listed ferments or inactivated probiotics, which by definition are not probiotics at all, since probiotics must be live. Traces of DNA from genuine probiotic species were detected in 68 percent of the toothpastes and 50 percent of the mouthrinses, but DNA is not the same as a living cell. Even after fermentation or pasteurization, bacterial remnants can retain intact DNA segments long enough to be amplified by PCR, which explains why molecular signals can persist in products that no longer contain a single living organism.

Only two toothpastes, Pro bident New Generation Toothpaste with Active Probiotics and STIM Probiotic Toothpaste, yielded colonies on MRS agar, and Sanger sequencing confirmed that the recovered species was Bacillus coagulans, matching their labels. Pro bident showed moderate viability at roughly 5.4 log10 colony-forming units per milliliter, while STIM reached about 8.2 log10, comparable to the BioGaia probiotic lozenge used as a positive control. The reason these two products succeeded where the others failed is almost certainly biological: Bacillus coagulans forms spores, and spores are notoriously resistant to heat, desiccation, preservatives, and the aqueous environment of a toothpaste tube. Lactobacilli and Bifidobacteria, the genera claimed by most other products, lack this survival advantage and are far more vulnerable to the water, preservatives, and active ingredients that make toothpastes and mouthrinses hostile habitats for bacteria.

The label analysis revealed additional problems beyond viability. None of the 22 products provided strain-level identification, which is crucial because clinical efficacy is strain-specific. Several products listed bacterial names that no longer correspond to current taxonomy. The genus Lactobacillus underwent a major revision in 2020, when many species were reassigned to newly established genera such as Limosilactobacillus, and Bacillus coagulans has since been reassigned to Heyndrickxia coagulans. One toothpaste even listed lactoferrin and lactoperoxidase, which are enzymes rather than microorganisms, as its probiotic content.

But presence and viability are only part of the probiotic equation. The third condition is a demonstrated health benefit, and here too the products fell short. The team grew multispecies oral biofilms on hydroxyapatite discs, mimicking the mineral surfaces of teeth, using a community of 14 oral bacterial species ranging from commensal streptococci to periodontal pathobionts such as Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans. When these biofilms were brushed with slurries of the two viable toothpastes for three minutes and then incubated for another 24 hours, there was no significant reduction in total bacterial load, and the relative abundance of commensal and pathogenic species remained unchanged compared with a phosphate-buffered saline control. Chlorhexidine, the positive control, did what it was supposed to do, confirming that the assay was sensitive enough to detect a real antimicrobial effect if one existed.

The researchers went further, isolating the Bacillus coagulans from the products and testing it directly against six common oral pathogens in co-culture experiments. After six hours of incubation, the probiotic showed no significant inhibitory effect on any of the tested pathogens. In fact, A. actinomycetemcomitans and Streptococcus sobrinus grew significantly more in the presence of B. coagulans than alone. The team also tested whether cell-free supernatants from B. coagulans cultures, which would capture any postbiotic, secreted antimicrobial compounds, could kill the pathogens, and found no such activity. pH measurements ruled out environmental acidification as a mechanism. In short, even the one probiotic that survived in these formulations showed no measurable antibacterial benefit under the tested conditions.

The authors are careful to note the limitations of their audit. They analyzed a single independent lot of each product, so the findings are specific to the batches tested and may not represent each brand as a whole. Manufacturing consistency, microbial viability, and product composition can vary between batches, and future studies should include multiple independent lots. The nutrient-rich laboratory media used in the co-culture experiments also do not fully reflect the conditions of saliva, which is far less generous to bacterial growth. Nevertheless, the consistency of the control samples across all replicates supports the reliability of the analytical pipelines.

What emerges from this study is a broader pattern. A previous audit by some of the same researchers, published in Frontiers in Microbiology in 2023, found similar problems with probiotic tablets and lozenges, including missing viable strains, incomplete strain information, and non-viable bacterial components. Taken together, the two studies suggest that the challenges of viability, strain identification, and labeling accuracy are not confined to one product category but represent a systemic issue across commercially available oral probiotic products. The authors conclude that probiotic toothpastes and mouthrinses, unlike probiotic lozenges, which remain the established delivery system for oral probiotics, may not consistently meet the established criteria for probiotics, and they call for a critical reassessment of both their use in scientific research and the commercial use of the term probiotic in product marketing. Until manufacturers can demonstrate that their products contain live, correctly identified, strain-level microorganisms in adequate amounts, and that those microorganisms confer a real benefit, the probiotic label on a toothpaste tube remains more marketing than microbiology.

Subject of Research: Probiotic toothpastes and mouthrinses: probiotic presence, viability, culturability, label accuracy, and effectiveness in vitro

Article Title: Probiotic toothpastes and mouthrinses: probiotic presence, viability, culturability, label accuracy, and effectiveness in vitro

Article References: Saghi, M., Van Holm, W., Zayed, N., Lauwens, K., Teughels, K., Boon, N., Bernaerts, K., & Teughels, W. (2026). Probiotic toothpastes and mouthrinses: probiotic presence, viability, culturability, label accuracy, and effectiveness in vitro. Frontiers in Oral Health, 7, Article 1936217. https://doi.org/10.3389/froh.2026.1936217

Image Credits: AI Generated

DOI: 10.3389/froh.2026.1936217

Keywords: probiotics, oral health, toothpaste, mouthrinse, microbiome, label accuracy, viability qPCR, 16S rRNA sequencing, oral biofilm, Bacillus coagulans, Frontiers in Oral Health, Probiotic