BackgroundHalitosis is defined as a foul odour emitted from the oral cavity. Many interventions have been used to control halitosis from mouthwashes to chewing gums. Probiotics have been reported as an alternative method to alleviate halitosis.ObjectiveThe present study aimed to investigate the effect of probiotics on halitosis from a time perspective.Design and methodsThis is a meta-analysis study performed in indexed databases up to February 2021. Randomised controlled trials that compared the effects of probiotics and placebo on primary outcomes (organoleptic (OLP) scores and volatile sulfur compound (VSC) levels) and secondary outcomes (tongue coating scores (TCS) and plaque index (PI)) were included. Data extraction and quality assessment were conducted independently by two reviewers. Publication bias and leave-one-out analyses were performed.ResultsThe standardised mean difference (SMD) and 95% CI were calculated to synthesise data. The data were subgrouped and analysed in the short term (≤4 weeks) and long term (>4 weeks) based on the follow-up time. Seven articles were included in this meta-analysis. The primary outcomes, OLP scores (SMD=−0.58; 95% CI −0.87 to –0.30, p<0.0001) and VSC levels (SMD=−0.26; 95% CI −0.51 to –0.01, p=0.04), both decreased significantly in the probiotics group compared with the placebo group in the short term. However, a significant reduction was observed only in OLP scores (SMD=−0.45; 95% CI −0.85 to –0.04, p=0.03) in the long term. No significant differences were observed in secondary outcomes. There was no evidence of publication bias. The leave-one-out analysis confirmed that the pooled estimate was stable.ConclusionsAccording to the results of this work, it seems that probiotics (eg,Lactobacillus salivarius,Lactobacillus reuteri,Streptococcus salivariusandWeissella cibaria) may relieve halitosis in the short term (≤4 weeks). The results of the biased assessment, limited data and heterogeneity of the clinical trials included might reduce the reliability of the conclusions.