Endosomal escape is often treated as though it were a scalar characteristic of a delivery material: a carrier is described as having high or low escape efficiency, and formulation optimization is subsequently organized around maximizing that property. This interpretation compresses several biologically distinct events into one label. Productive cytosolic delivery requires cellular internalization, entry into a permissive intracellular trajectory, appropriate carrier restructuring, timely cargo–carrier dissociation, interaction with an endosomal membrane, sufficient membrane destabilization without disproportionate injury, and survival of competing recycling and degradative pathways. Failure at any one of these transitions can produce the appearance of poor “escape,” even when the material itself retains membrane-active capacity. Conversely, strong membrane perturbation can occur without efficient liberation of usable cargo. This Perspective therefore reframes endosomal escape as a systems bottleneck generated by the alignment of carrier state, cargo state, compartment identity, cell type, dose, and time. Evidence from quantitative localization, split-luciferase assays, galectin reporters, nanoscale imaging, lipid-nanoparticle structural studies, and triggered endosomal-release systems is used to separate measurable states that are frequently conflated. A proposed systems model is developed in which productive escape is an emergent transition rather than a universal material constant. The resulting framework changes how escape should be measured, compared, optimized, and validated in nucleic-acid delivery.
IJPRAS
