Social media impacts people’s wellbeing in diferent ways, but relatively little is known about
why this is the case. Here we introduce the construct of “social media sensitivity” to understand
how social media and wellbeing associations difer across people and the contexts in which these
platforms are used. In a month-long large-scale intensive longitudinal study (total n= 1632; total
number of observations = 120,599), we examined for whom and under which circumstances social
media was associated with positive and negative changes in social and afective wellbeing. Applying
a combination of frequentist and Bayesian multilevel models, we found a small negative average
association between social media use AND subsequent wellbeing, but the associations were
heterogenous across people. People with psychologically vulnerable dispositions (e.g., those who
were depressed, lonely, not satisfed with life) tended to experience heightened negative social media
sensitivity in comparison to people who were not psychologically vulnerable. People also experienced
heightened negative social media sensitivity when in certain types of places (e.g., in social places,
in nature) and while around certain types of people (e.g., around family members, close ties), as
compared to using social media in other contexts. Our results suggest that an understanding of the
efects of social media on wellbeing should account for the psychological dispositions of social media
users, and the physical and social contexts surrounding their use. We discuss theoretical and practical
implications of social media sensitivity for scholars, policymakers, and those in the technology
industry.