Status quo, challenges and future directions of hydrogen medicine

The hydrogen molecule (H 2 ) has distinctive characteristics and advantages in broad-spectrum anti-inflammation, high biosafety and strong tissue permeability, exhibiting therapeutic potential in numerous diseases associated with inflammation and oxidative stress. In this perspective, we attempt to show a clear picture of the status quo, challenges and future directions of hydrogen medicine in terms of biological mechanisms, metabolic behaviors, and delivery materials and techniques of H 2 . Firstly, we present the current understanding of biological effects and corresponding mechanisms of H 2 involving the recognition of H 2 molecular target, and point out the challenge of explaining the multifaceted biological behaviors of H 2 . Then, to explore and understand the metabolic behaviors of H 2 , we summarize current H 2 detection techniques and identify the experimental validation of high biocarriers-crossing ability of H 2 by virtue of a freshly developed H 2 molecular bioprobe. Next, to develop the strategies for enhancing the efficacy of hydrogen therapy, we demonstrate the evolution of H 2 -delivery materials from H 2 carriers to hydrolytic and catalytic H 2 -generating materials. Finally, we outline the future development directions of hydrogen medicine.