Digital technology is embedded in daily life, and growing evidence suggests that evening and bedtime screen engagement may disrupt sleep in young adults. Associations appear stronger for bedtime exposure and problematic or addiction-like patterns of use than for total screen time alone. This review aims to synthesize current evidence on the relationship between smartphone and social media use and sleep outcomes in young adults, with particular attention to the timing of device use, problematic digital engagement, and psychological or behavioral factors that may influence sleep. A narrative literature review was conducted using a broad, non-systematic search of PubMed, Scopus, Web of Science, and Google Scholar. Observational, longitudinal, experimental, or interventional studies and higher-level syntheses were included when they contributed to conceptual understanding of the screen-sleep relationship. Evidence was organized thematically across domains, including overall associations, bedtime and in-bed use, problematic and addictive behaviors, bedtime procrastination, psychological mediators (rumination and fear of missing out), chronotype, objective exposure and sleep measures, content versus duration, and cross-cultural consistency. Across diverse populations and study designs, digital media use was consistently associated with poorer sleep outcomes, including reduced sleep quality, delayed sleep onset, shorter sleep duration, and daytime dysfunction. Bedtime and nighttime use showed stronger associations than general daily exposure, supporting sleep displacement and circadian disruption as key pathways. Problematic smartphone and social media use demonstrated particularly robust links with poor sleep and insomnia-related symptoms, and longitudinal evidence suggested bidirectional relationships between problematic phone use, impaired sleep, and depressive symptoms. Bedtime procrastination emerged as a central behavioral mediator, while rumination and fear of missing out contributed to cognitive-emotional arousal that sustains sleep disruption. Objective smartphone tracking and wearable sleep measures generally supported associations between nighttime phone activity and worse sleep, although short-term panel studies assessing brief exposure windows reported largely null effects. Experimental studies of short-term social media abstinence and structured digital detox interventions showed improvements in sleep quality and psychological well-being. Evidence indicates that sleep dysregulation in young adults is most strongly linked to bedtime screen exposure and problematic or compulsive digital engagement rather than screen time alone. Digital sleep hygiene strategies that reduce in-bed use and address problematic smartphone behaviors may improve sleep and well-being. Future research should prioritize longitudinal and intervention designs, clearer exposure definitions capturing habitual bedtime behaviors, and greater use of objective tracking to strengthen causal inference.
