Recent research has documented the relationship between the promotion of ‘ideal’, ‘fit’ bodies in social media, body image and associated body concerns and conditions. This article expands this scholarship, focusing specifically on gender, body dissatisfaction and social media. Thus far, body disaffection has mostly been understood through a psychological framing, as a pathology residing within an individual and strongly associated with poor body image because of internalizing media images. In this paper, drawing on feminist new materialism, I offer a framing of body disaffection as a relational phenomenon. The paper draws on a mixed method study in England, with over 1000 young people examining their experiences with a range of digital health technologies. I focus specifically on their engagement with social media, to explore the relationship between ideal images and body concerns. Far from being a simple process of internalization of negative perceptions or image one has of their body, disaffection is formed through the body via a complex process of entanglement with social media and other elements. I outline how disaffection materialises as part of an assemblage of elements, including discourses, humans, bodies, digital objects and platforms. The paper reveals how entanglements with social media can generate powerful affects such as shame, pleasure and belonging along gendered lines, which may have significant implications for young people’s relationships with their bodies. I analyse how social media events focused on the ‘transformation’ of bodies generate powerful affects, which open or limit capacities for what ‘boys’ or ‘girls’ bodies might become in deeply gendered and sometimes harmful ways.