Young adults are currently the loneliest demographic in the UK and other Western countries, yet little is known about how they see the causes of their loneliness. Thus, the objective of this study is to explore the subjective causes of loneliness among young adults (18-24 years old), particularly those of lower socio-economic status (SES) who are in employment, renting and living in the most deprived areas, since they are the loneliest in the UK. Utilising a free association technique and thematic analysis, and embedded in a phenomenological framework, the subjective causes of loneliness in a matched sample of 48 young adults in the four most deprived boroughs of London are found to cluster around five themes: The Feeling of Being Disconnected, Contemporary Culture, Pressure, Social Comparison and Transitions Between Life Stages. Disconnection arises from feeling one does not matter, is not understood or is unable to express oneself. Challenges pertaining to social media and materialism in contemporary culture contribute to loneliness as does pressure associated with work, fitting in and social comparison. Social media play a major role in exacerbating these experiences. Finally, transitions between life stages such as breakups, loss of significant others and transitory stages to do with education and employment are felt to cause loneliness. The findings suggest potential avenues for loneliness reduction.