The implementation of functionalities inspired by ephemerality represents a new and promising direction for social media platform providers to ensure active user participation. Social media platforms that already rely on ephemerality show increased activity rates. However, ephemerality represents a whole new principle in the social media context; and its impact on user perceptions and behaviours has hardly been explored. Building on an exploratory research approach, we seek to develop an in-depth understanding of how and why perceived ephemerality affects user behaviour. Based on 37 interviews with users of ephemerality-based platforms and drawing on a thematic analysis, we depict the promising nature of ephemerality by revealing its positive impact on user behaviour, such as an increase in users’ willingness to share information. We found that users’ control perceptions help to explain this positive relationship. However, and contrary to existing knowledge, we found that, in specific conditions, perceived ephemerality can negatively affect user behaviour. This adverse effect can be explained by users’ loss perceptions as an underlying cognitive mechanism. From a practical perspective, our findings highlight the need to keep the delicate balance of potential upsides and downsides of ephemerality when implementing functionalities.