AbstractMovements like “Fridays for Future” have heightened attention to the need for sustainability, particularly among Generations X, Y, and Z. However, the consumption of fast fashion and so‐called ultra‐fashion products—an ecologically harmful business model—continues to gain momentum, especially among young consumers, not least due to fear of missing out (FOMO). FOMO is well‐known among marketing professionals as a strong trigger for frequently recurring buying behavior. Over the past 5 years, scholars have become increasingly interested in how FOMO triggers buying behavior and have begun to incorporate FOMO in their cognitive models. However, the influence of FOMO on individual fashion purchases and the relationship between brand credibility and sustainable fashion production is not yet well understood. Utilizing cross‐sectional data from three distinct samples in Switzerland and the United States, our study, which included over 650 participants, reveals that brand credibility and FOMO exert direct influences on consumers' purchase intentions for fast fashion products. We identify that FOMO has a negative moderating effect on the relationship between brand credibility and fast fashion purchase intentions. Suggesting that consumers with strong FOMO are less interested in brand credibility when making a purchase decision than those without FOMO. Additionally, we demonstrate that our findings apply to both fast and slow fashion, the latter encompassing sustainably produced fashion. Ultimately, we provide novel empirical evidence of FOMO's influence on buying behavior and shed light on the complex interplay between brand credibility, sustainability, and consumer behavior in the fashion industry.