The harmful effects of solitary confinement have been established in a variety of direct observations and empirical studies that date back to the nineteenth century, conducted in many different countries by researchers with diverse disciplinary backgrounds. This Essay argues that these effects should be situated and understood in the context of a much larger scientific literature that documents the adverse and sometimes life- threatening psychological and physical consequences of social isolation, social exclusion, loneliness, and the deprivation of caring human touch as they occur in free society. These dangerous conditions are the hallmarks of solitary confinement. Yet they are imposed on prisoners in far more toxic forms that exacerbate their harmful effects, are incurred in addition to the adverse consequences of incarceration per se, and operate in ways that increase their long-term negative impact. This broader empirical and theoretically grounded scientific perspective expands the harmfulness narrative about solitary confinement and argues in favor of much greater restrictions on its use.