Background and aims:
Stress responsivity and habitual behaviors are related to problematic online buying-shopping (BSh) according to the Interaction of Person-Affect-Cognition-Execution (I-PACE) model. This study aimed to investigate if symptoms of problematic online BSh, an experimental indicator of habitual behavior and the interaction of potentially habitual behavior and stress responsivity predict everyday use of buying-shopping platforms.

Participants:
The study comprised participants with risky (n = 27) and non-problematic (n = 28) online BSh.

Design and measurements:
A Pavlovian-to-instrumental transfer paradigm with devaluation (PIT-dev) was administered. Changes of cortisol stress level after an acute stressor were measured. A subsequent end-of day ambulatory assessment captured use time of buying-shopping platforms for 14 days. Multilevel analyses with collapsed groups were computed.

Findings:
Symptoms of problematic online BSh were related with higher everyday use of shopping platforms. The PIT-dev effect solely was not associated with use time of buying-shopping platforms but interacted with cortisol stress responsivity on use time. If stress responsivity was low, PIT-dev effect negatively influenced use time. If stress responsivity was high, PIT-dev effect showed positive associations with use time. The latter effect was more pronounced in persons with more problematic BSh.

Conclusions:
The findings indicate an interplay between stress responsivity and habitual behaviors on everyday use of buying-shopping platforms, aligning with the I-PACE model. Future research should investigate long-term longitudinal effects of habit formation in the development of problematic online BSh. Clinical implications include building and implementing functional habits for stressful events to counteract shopping-specific habits facilitated by stress.