Background: This conceptual article reports a structured narrative review that repositions fear of missing out (FOMO) as a situational mediator between flash sale promotions and impulse buying in online marketplaces. Flash sales bundle a price cut with a countdown and a stated stock limit, yet discount depth alone does not explain why some consumers abandon their purchase plans while others delay.Objective: The review pursued three objectives, namely to delimit the constructs that link promotional stimuli to impulsive responses, to specify the evidence required before mediation may be claimed, and to translate both into a promotion evaluation framework.Method: Literature was retrieved from Scopus, ScienceDirect, SpringerLink, Taylor and Francis Online, Google Scholar, and Garuda using four Boolean search strings, screened against explicit inclusion criteria, and reduced to a full-text corpus in which empirical tests of flash sale, scarcity, FOMO, and impulse buying relationships were separated from theoretical and methodological sources. Synthesis followed an integrative review logic, and every extracted claim was labelled as source evidence, author interpretation, or untested proposition.Results: Three findings emerged. Empirical results converge on a positive scarcity to FOMO to impulse buying sequence in which mediation is reported more often as partial than as full. That convergence rests largely on cross-sectional, self-report, student-dominated designs, so the sequence remains associational rather than causal. General FOMO and situational FOMO behave differently and should not share one instrument.Conclusion: The article contributes an integrated construct, measurement, and evaluation framework together with a testable model.