This research aims to design a green brand model and examine its impact on the loyalty of Generation Z consumers within the cosmetics and personal care industry, with a specific focus on the Sinere brand in Iran. Employing an applied and descriptive analytical approach, this study adopts a qualitative research design. The statistical population comprises managers, specialists, and experts actively engaged in Iran’s cosmetics and personal care sector, particularly those associated with the Sinere brand. Participants were selected through snowball sampling, and data collection continued until theoretical saturation was achieved, resulting in a final sample of 15 experts. The primary data collection instrument was semi structured interviews, and the collected data were analyzed using the grounded theory method. The analysis proceeded through three coding stages: open coding (yielding 85 initial codes), axial coding (categorizing codes into concepts and categories), and selective coding (developing the final model). The findings are presented in the form of six main categories—namely, causal conditions, contextual conditions, core phenomena, intervening conditions, strategies, and consequences—comprising 24 sub categories. The results indicate that green brands significantly enhance Generation Z’s loyalty by improving product quality and fostering positive customer experiences. Furthermore, the brand’s environmental commitment and the promotion of green values play a pivotal role in increasing consumer trust, which in turn serves as a fundamental prerequisite for positive word of mouth and attitudinal loyalty. In other words, the simultaneous interplay of cognitive factors (perceived green authenticity) and affective factors (environmental values) distinguishes pioneering brands from competitors in the minds of young consumers. Consequently, by focusing on innovative green strategies and adhering to environmental principles, the Sinere brand can sustain its competitive position and customer loyalty, while also offering an effective model for other brands operating in this industry.