Smartphone Screen Time, Sleep Quality, and Headache in Young Adults Presenting to the Emergency Department: A Case–Control Study

Background: Smartphone screen exposure has increased substantially among young adults and has been associated with headache and sleep disturbances. This study aimed to investigate the associations between smartphone screen time, headache severity, sleep duration, and sleep quality in young adults presenting to the emergency department with headache. Methods: This single-center case–control study was conducted in the emergency department of a tertiary university hospital between November 2025 and April 2026. A total of 300 participants aged 18–40 years were enrolled, including 150 patients with headache and 150 controls without headache. Daily smartphone screen time was obtained from the built-in smartphone records for the preceding completed seven-day period, headache severity was assessed using the 11-point Numeric Rating Scale, and sleep quality was evaluated using the validated Turkish version of the Single-Item Sleep Quality Scale. Results: Participants with headache had longer smartphone screen time (7.0 vs. 5.0 h/day; p < 0.001), shorter sleep duration (7.0 vs. 8.0 h/day; p = 0.005), and poorer sleep quality (5.0 vs. 7.0; p < 0.001) than controls. Screen time correlated with headache severity (ρ = 0.430, p < 0.001) and inversely with sleep quality after adjustment for study group (partial ρ = −0.185, p = 0.001). Nonlinear multivariable modeling showed an association with headache presentation (p < 0.001); relative to 6 h/day, the aOR at 7 h/day was 8.83 (95% CI: 5.00–15.60), with a plateau at higher exposures. Conclusions: Longer device-recorded smartphone screen time was associated with headache presentation and severity in young adults. Participants with headache also reported poorer sleep quality and shorter sleep duration. These findings suggest relevant associations between smartphone exposure, sleep, and headache but do not establish causality or a clinical screen-time threshold. Prospective studies are warranted.