This essay aims to discuss the flexibilization of work, which has been accentuated during the COVID-19 pandemic, leading to an expansion of precarious work. Additionally, the essay seeks to explore theoretical models and methodological challenges for the study of precarious work, its dimensions, and its effects on workers’ health. The health and economic crisis has heightened the social vulnerability of workers, introduced by the global flexibilization and the Brazilian Labor Reform. The setbacks materialize in precarious work, a multidimensional construct that encompasses the characteristics of this flexibilization in its three dimensions: (1) unstable work relationships resulting from insecure hiring, temporary contracts, involuntary part-time work, and outsourcing; (2) inadequate and unstable income; and (3) insufficient rights and protection, with reduced collective representation of workers, resulting in low power to react to degrading working conditions, lack of social security, and setbacks in regulatory support for labor safety. Repercussions of precarious work on health − work accidents, musculoskeletal and mental disorders - are evidenced in epidemiological studies, highlighting the theoretical and methodological limitations that still exist. The conclusion is that if the current bases of social protection and work insertion for workers are maintained, the future will see an expansion of precarious work. Thus, highlighting the causal relationships between precarious work and health is a contemporary challenge of the research and public policy agenda that is imposed upon society, with a focus on workers’ health services.