Tehran University of Medical Sciences International Journal of Occupational Hygiene 2008-5109 16 2 2025 08 30 20 24 Neda Mehrparvar Department of Occupational Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Soqrat Omari Shekaftik Department of Occupational Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran | Students’ Scientific Research Center, Tehran University of Medical Sciences, Tehran, Iran 2025 02 01 2025 04 07 Health risk assessment of activities involving nanomaterials is a basic and necessary step toward reducing exposure to nanomaterials and, consequently, minimizing the effects resulting from such exposure. Health risk assessment methodologies in the presence of chemical substances, including nanomaterials, can be divided into three major groups: quantitative, semi-quantitative, and qualitative methods. The quantitative assessment of risks associated with activities involving nanomaterials faces a series of inherent limitations, which have led to its limited acceptance. The absence of well-established and universally agreed-upon occupational exposure limits, and the uncertainties surrounding the effects of nanomaterials on humans, are some of these limitations. Qualitative approaches, based on precautionary principles and expert judgment, offer flexible, context-sensitive evaluation, whereas semi-quantitative approaches have a more ordered framework that nonetheless allows for adaptability in the balancing of numerical analysis with qualitative insight. Yet, parallel efforts toward the development and refinement of quantitative methods must not be forsaken, as such methods are considered indispensable for the future to realize more accurate and reliable risk assessments. This will give a more holistic and realistic assessment of nanomaterial risks due to this dual approach. https://ijoh.tums.ac.ir/index.php/ijoh/article/view/666 https://ijoh.tums.ac.ir/index.php/ijoh/article/download/666/845