Preventable in-body hydrogen explosions from high-concentration H 2 inhalers in Japan—Switch to safe, low-concentration hydrogen therapy

Background With the growing recognition of the medical applications of hydrogen, hydrogen gas inhalers are increasingly used in clinics and other healthcare settings. However, hydrogen is highly explosive, and numerous explosion incidents involving these inhalers have been reported. Objectives This study evaluates the safety risks of high-concentration hydrogen inhalers (67%–99.99% v/v H 2 ) following multiple device explosions and a documented pulmonary explosion case, and to determine an optimal concentration balancing safety and efficacy. Methods We analyzed device explosion incidents recorded by the Consumer Affairs Agency of Japan and an in-body hydrogen explosion case reported in a 2024 scientific paper, and subsequently discussed the factors contributing to these accidents based on the explosive properties of hydrogen gas. Results High-concentration inhalers (>10% v/v H 2 ) pose a substantial explosion risk, as confirmed by multiple device failures reported by Japan’s Consumer Affairs Agency and a 2024 in-vivo pulmonary explosion case. Limiting hydrogen to ≤10% v/v maintains efficacy for intracellular hydroxyl radical scavenging while staying below the lower explosive limit. Conclusion Two critical preventable hazards exist with high-concentration hydrogen therapy: external device explosion and internal airway detonation. Immediate transition to low-concentration (≤10% v/v H 2 ) inhalers is strongly recommended, as they provide effective concentration while eliminating life-threatening risks, ensuring patient safety without compromising clinical outcomes.