Their 2D nanosheets tend to undergo rapid degradation in aqueous media or humid environments, resulting in the formation of their respective metal oxides. Even the most stable and the most studied Ti 3 C 2 T x MXenes show notable degradation after being dispersed in water for a week. While the lifespan of dried freestanding Ti 3 C 2 T x -MXene layers can be extended even for years, films of different compositions can degrade when stored at ambient conditions. Recent studies have identified two major culprits causing the degradation of MXenes: water and oxygen molecules. The reported exponential decay in the rate of oxidation of MXenes exposed to a humid environment suggests the existence of active sites catalyzing the oxidation reaction. While these sites are saturated, the reaction slows down. Several studies hypothesized that edges of MXenes are more prone to oxidative degradation, while others suggested that degradation starts at the basal plane of MXenes and that the presence of defects should be considered a possible source of instability. Since the conflicting opinions on the origin of material degradation can lead to different degradation prevention strategies, revealing the active sites catalyzing the degradation process is pivotal for the effective design and implementation of MXene-based materials.