Recent Advancements in Wearable Hydration Monitoring Technologies: A Scoping Review of Sensors, Trends, and Future Directions (Preprint)

Abstract

BACKGROUND Monitoring hydration is crucial for maintaining health and preventing dehydration-related is-sues. Wearable devices offer a promising method for continuously tracking hydration levels. Despite the popularity of wearable technology in health research, its application for hydration monitoring is not extensively studied, and clear design guidelines are lacking. This scoping review aims to fill this gap by analyzing existing research trends and the potential impact of wearable technologies for hydration monitoring. OBJECTIVE This review comprehensively analyzes recent advancements in wearable hydration monitoring technologies, focusing on their capabilities, limitations, and research and prototype designs. It explores different sensors and technologies for tracking hydration, compares their ad-vantages and disadvantages, identifies trends in wearable hydration monitoring devices, assesses their accuracy and reliability compared to established benchmarks, and identifies commercially available products to bridge research findings with practical use. METHODS Following PRISMA guidelines, a scoping review was conducted to explore the breadth and variety of technological approaches in hydration monitoring research. A systematic search across Pubmed, IEEE Xplore, and Google Scholar was performed using a versatile search syntax. Studies published since 2014 focusing on non-invasive, portable hydration monitoring systems utilizing physiological biomarkers were included. RESULTS The review included 63 articles selected from 156 studies for synthesis analysis. The literature was categorized based on sensor types, including electrical, optical, thermal, microwave, and multimodal sensors. Most studies explored hydration’s effects on physiological parameters, with some examining hydration status during physical activity or in various environmental conditions. Commercially available products from eight companies were also evaluated for technological features, functionalities, and applications. The dominance of electrical sensors in re- search was noted, leveraging their ease of use and integration into wearables. While fewer in number, optical methods exhibited precision and provided molecular-level in-sights. The emergence of multimodal sensors indicated a trend toward combining technologies for better ac- curacy. Other sensors, such as thermal and microwave-based variants, found unique niches. The prevalence of optical-based wearables in the market suggests their growing acceptance due to cost-to-precision effectiveness. CONCLUSIONS Wearable hydration monitoring devices offer real-time hydration assessments, but challenges remain in reliability, accuracy, and applicability across diverse populations and conditions. Future directions include standardized protocols, extensive clinical studies, sensor miniaturization, and improved wearability. Multimodal systems combining various sensors with AI-driven analysis offer potential for personalized hydration management. This review provides detailed insights into sensor technologies’ strengths and challenges, paving the way for practical solutions in skin hydration monitoring.