Recent Advances in Flexible Humidity Sensors for Sleep-Disordered Breathing Monitoring

Flexible humidity sensors show great promise for wearable respiratory monitoring in sleep-disordered breathing, yet practical deployment is constrained by bottlenecks: the sensitivity-speed trade-off, environmental interference, and self-powered integration. Responding to the demand for enhanced performance and integration, this review surveys recent advances in flexible humidity sensors for respiratory monitoring, emphasizing sensing mechanisms, nanomaterial systems, and fabrication strategies. According to the signal transduction mode, existing studies are classified into three categories, including resistive/impedance type, capacitive type, and voltage type, and the breakthroughs and limitations of each in material design and structural optimization are reviewed. Representative applications including respiratory rate monitoring, SDB alert systems, and smart face masks are highlighted, alongside emerging trends in structural synergy and mechanistic fusion. Finally, key challenges and future research directions are identified. This review provides a practical reference for designing high-performance flexible humidity sensors, accelerating their transition from laboratory prototypes to home-based health management.