Table 1

Characteristics of the included studies

Study	Type	Halitosis criterion	Subject age	Clinical parameters	Probiotics administration (vehicle, strains and frequency)	Follow-up
Mousquer et al61	RCT Placebo double-masked parallel	OLP score ≥1	29 ≥18	OLP VSC TCS	Gum including 1 billion CFU Lactobacillus salivarius G60 taken twice per day	Baseline 2 weeks
Lee et al60	RCT Placebo double-blind parallel	VSC ≥1.5 ng/10 mL	68 20–39	OLP VSC (H₂S, CH₃SH, C₂H₆S)	800 mg tablet containing 1.0×10⁸ CFU/g Weissella cibaria taken once per day	Baseline 4 weeks 8 weeks
He et al42	RCT Placebo double-blind parallel	OLP score ≥2 VSC ≥150 ppb	28 23–44	OLP VSC TCS PI	Tablet containing 1×10⁹ CFU Streptococcus salivarius K12 taken twice per day	Baseline 4 weeks
Keller et al58	RCT Placebo double-blind crossover	OLP score >1	25 19–25	OLP VSC	Chewing gum containing Lactobacillus reuteri DSM 17938 and Lactobacillus reuteri ATCC PTA 5289, both with a concentration of 1×10⁸ CFU taken twice per day	Baseline 2 weeks
Suzuki et al57	RCT Double-blind placebo-controlled crossover	OLP score ≥1.5	23 22–67	OLP VSC (H₂S, CH₃SH, C₂H₆S) PI TCS	Tablet containing 6.7×10⁸ CFU Lactobacillus salivarius WB21 and 280 mg xylitol taken three times per day	Baseline 2 weeks
Penala et al59	RCT Placebo double-blind parallel	OLP score >2	29 25–59	OLP PI	Capsule mixture including Lactobacillus salivarius (2×10⁹ CFU) and Lactobacillus reuteri (2×10⁹ CFU) dissolved in 10 mL distilled water to rinse for 1 min twice daily	Baseline 4 weeks 12 weeks
Kim et al49	RCT Placebo double-blind parallel	OLP score ≥2 VSC ≥0.15 ng/mL	58 20–70	VSC (H₂S, CH₃SH, C₂H₆S) OLP	Bag of powder mixture including Weissella cibaria CMU (1.0×10⁸ CFU) melted in the mouth once per day	Baseline 2 weeks 4 weeks 8 weeks

CFU, colony forming units; C₂H₆S, dimethyl sulfide; CH₃SH, methyl mercaptan; H₂S, hydrogen sulfide; OLP, organoleptic; PI, plaque index; RCT, randomised controlled trial; TCS, tongue coating score; VSC, volatile sulfur compound.