Bacillus species, particularly Bacillus subtilis, have been investigated for their potential role in managing halitosis (bad breath) due to their probiotic properties. Several studies have demonstrated that some Bacillus strains can inhibit the growth of bacteria associated with volatile sulfur compound (VSC) production, which are key contributors to oral malodor. The proposed mechanism involves Bacillus species producing antimicrobial peptides or enzymes that reduce populations of odor-causing bacteria such as Porphyromonas gingivalis and Fusobacterium nucleatum. For example, a 2016 study in the Journal of Breath Research reported that a Bacillus-based probiotic mouth rinse reduced VSC levels and improved subjective measures of breath odor in a small human trial.

However, the evidence base is limited. Most studies involve small sample sizes, short durations, or are conducted in vitro or in animal models. There are few well-controlled, large-scale clinical trials evaluating the efficacy of Bacillus probiotics for halitosis in humans. In addition, most probiotic products for oral health typically use strains such as Streptococcus salivarius or Lactobacillus species, with Bacillus-based products being less common but emerging. Thus, while there is some scientific support for Bacillus use in halitosis, the evidence is still preliminary and not robust.