For nearly two decades, the medical benefits of molecular hydrogen have been shrouded in mystery, with many researchers relying on a flawed “selective antioxidant” hypothesis. A groundbreaking 2025 discovery identifying the Rieske iron-sulfur protein in mitochondrial Complex III as a key target finally explains how hydrogen actually works: it acts as a mitochondrial signaling molecule and a hormetic stressor. This article unpacks the new science, clarifies the limitations of the current clinical evidence, and cuts through the marketing hype surrounding hydrogen therapies.