The growing popularity of TikTok Shop Live has created new opportunities for interactive product promotion while potentially encouraging spontaneous purchasing behavior. This study examines the relationship between perceived interactivity and impulse buying among female Generation Z consumers purchasing skincare products through TikTok Shop Live, with urge to buy impulsively as a mediating variable. Drawing on the Stimulus–Organism–Response (S-O-R) framework, the study conceptualizes perceived interactivity as a stimulus, urge to buy impulsively as an internal psychological state, and impulse buying as a behavioral response. A quantitative approach was employed using a cross-sectional survey of 200 female Generation Z consumers aged 18–29 residing in Jakarta. Respondents were selected through purposive sampling based on their experience watching skincare-related TikTok Shop Live sessions within the previous three months and purchasing skincare products through the platform within the previous six months. Data were analyzed using Partial Least Squares Structural Equation Modeling (PLS-SEM) with SmartPLS. The results indicate that perceived interactivity is positively associated with urge to buy impulsively (β = 0.573, p < 0.001) and impulse buying (β = 0.471, p < 0.001). Urge to buy impulsively also exhibits a positive relationship with impulse buying (β = 0.372, p < 0.001). Furthermore, urge to buy impulsively significantly mediates the relationship between perceived interactivity and impulse buying (β = 0.213, p < 0.001), with the direct relationship remaining significant, indicating complementary partial mediation. These findings contribute to the application of the S-O-R framework in explaining impulse buying in livestream commerce by demonstrating the role of consumers’ spontaneous purchase urges as one psychological mechanism linking interactive experiences to actual purchasing behavior. Practically, the findings highlight the importance of responsive, timely, and relevant seller interactions in facilitating consumer engagement and purchasing decisions during TikTok Shop Live sessions.