The rising research interest in personalized medicine promises to revolutionize traditional medical practices. This presents a tremendous opportunity for developing wearable devices toward predictive analytics and treatment. In this talk, I will introduce our efforts in developing fully-integrated skin-interfaced sweat biosensors for non-invasive molecular analysis. Such wearables can autonomously access sweat across activities and continuously measure a broad spectrum of analytes including metabolites, electrolytes, nutrients, hormones, and drugs. Laser-engraving and inkjet printing are used to manufacture these nanomaterials-based biosensors at large scale and low cost. The clinical value of our wearable systems is evaluated through multiple human studies involving both healthy and patient populations toward nutritional monitoring, disease diagnosis, mental health assessment, and drug personalization. This talk will feature our recent works on self-powered battery-free electronic skins for wireless health monitoring. These wearable devices could open the door to a wide range of personalized monitoring, diagnostic, and therapeutic applications.