The purpose of this overview was to present historical data on the discovery of hydrogen and a brief summary of its physical properties that form the basis for its use in aeronautics. Information is provided on the use of hydrogen, a biologically neutral molecule, in medicine as a diagnostic indicator for penetrating wounds of the gastrointestinal tract, the determination of local blood flow using the hydrogen clearance method, the use of the hydrogen breath test for the diagnosis of malabsorption and carbohydrate intolerance, achlorhydria, the diagnosis of bacterial overgrowth syndrome, the assessment of biodegradation of magnesium-containing implants, the orocecal transit time, and during deep-sea diving. The reasons for the sharp increase in the doctors’ interest in studying the biological role of hydrogen after the discovery of its antioxidant properties by a group of Japanese scientists (2007) are analyzed. In order to increase antioxidant protection of the body, data from recent research on ways to increase its concentration in the body through the supply of exogenous gas by inhalation or by administering hydrogen-rich water or saline solution is presented. Particular attention is paid to a critical analysis of studies on the kinetics of hydrogen by different routes, its concentration in blood and tissues, inhalation, and the use of hydrogen-rich water. Based on an analysis of publications, that the use of molecular hydrogen to relieve oxidative stress in the tissues of the intestines, liver and lungs is most promising, since its highest concentration is found in these tissues. Fermentation of carbohydrates has also been shown to increase the production of hydrogen by the intestinal microbiota. Considering that a large number of molecular hydrogen generators appeared on the market, the data on the requirements for their safety are summarized. Considerations on the use of molecular hydrogen for the purpose of antioxidant protection of the body in cardiology, gastroenterology, pulmonology, and other areas of medicine are based on modern views on the mechanisms of antioxidant, anti-apoptotic, cytoprotective, and anti-inflammatory effects of hydrogen. Particular attention is paid to the analysis of experimental and clinical research on the use of hydrogen in acute and chronic lung lesions, therapy of acute and chronic COVID-19 infection.Conclusion. Based on an analysis of the literature and our own data, a conclusion was drawn on the safety and prospects of the clinical use of molecular hydrogen in a wide range of concentrations in many diseases with the pathogenesis based on oxidative stress. In particular, the need for additional research was highlighted to clarify the regimen, frequency, duration and concentrations of hydrogen used, and a personalized approach to the combination of endogenous (from the intestinal microbiota) and exogenous hydrogen in various diseases.
