You Can Monitor Your Hydration Level Using Your Smartphone Camera

This study presents the first demonstration of a smartphone-based, noninvasive method for dehydration monitoring, effectively transforming a regular mobile device into a virtual medical instrument. The proposed technique requires users to record a short video of their fingertip using the smartphone camera while covering the lens with the index finger. This enables the extraction of a photoplethysmography (PPG) signal, which captures peripheral blood volume fluctuations that correlate with the changes in hydration status. A key challenge in nonclinical dehydration assessment is the absence of biochemical ground truth. To address this, we conducted a controlled study with 50 fasting individuals over a 13-h period. Fingertip videos were recorded four times at regular intervals during fasting, leveraging the monotonic decline in hydration to label data as fully hydrated, mildly dehydrated, moderately dehydrated, and severely dehydrated. We preprocessed the collected PPG signals and used them to train a range of artificial intelligence (AI) models for classifying hydration status on a 1–4 scale. In addition, we used SHapley Additive exPlanations (SHAP) to interpret model decisions. This method, being a nonbiochemistry-based approach, does not intend to replace clinical dehydration diagnostic procedures. Rather, it is proposed as a complementary, first-aid screening tool for use in nonhospital environments. Our findings indicate that smartphones can offer rapid, cost-effective, and user-friendly hydration monitoring, paving the way for scalable, patient-centric health solutions. This proposed method is anticipated to be an essential ingredient of smart homes, wearable health ecosystems, and the broader vision of intelligent cities.