<p>The pervasive presence of nanoplastics, particularly those originating from everyday sources, has emerged as a critical public health and environmental concern. Despite an expanding body of research, a disproportionate emphasis on the ‘nano’ aspect remains—specifically, the size and size distribution—while the chemical composition of these particles is largely overlooked or limited to the polymer identity. This gap in understanding hinders a comprehensive evaluation of the environmental behaviour and biological interactions of nanoplastics. Here we explore the diverse origins of nanoplastics, focusing on their chemical diversity and the associated implications for their environmental fate and behaviour. We highlight the often-neglected primary nanoplastics generated during production processes, such as low-molecular-weight oligomers and additives in polymeric forms, distinguishing them from secondary nanoplastics formed through the degradation of the plastic polymer matrix. We discuss how the dual forms of nanoplastics (aggregates or individual particles) affect their fate and implications. Finally, we propose recommendations for advancing nanoplastics research, emphasizing the need for molecular weight characterization, the incorporation of primary nanoplastics in analyses and the development of proactive strategies to mitigate nanoplastic pollution at its source.</p>