Objective To systematically review evidence regarding the efficacy of EOs and their constituents in the treatment of halitosis. Methods Three databases were searched for randomized controlled trials (RCTs) published between 1st January 2000 and 31st December 2020 wherein EOs and their constituents, alone or combined with mechanical oral hygiene procedures, were used and objective or subjective assessment of halitosis was performed. Results From a total of 162 articles, nine RCTs were included. All the EOs tested showed higher efficacy than placebo, were found to be as effective as quaternary ammoniums, metal salts and phenols, but less effective than chlorhexidine in controlling oral malodour. Considerable heterogeneity was found between the trials and the level of bias was unclear in most of the studies (6/9). Conclusion Low to very low certainty evidence suggest some benefits of EOs and EO constituents in reducing oral malodour. However, more well-designed studies are still required before clear recommendations can be made on the safety and efficacy of oral application of EOs and EO constituents in the management of halitosis.