# Molecular Hydrogen: A Promising Adjunctive Strategy for the Treatment of the COVID-19.
> COVID-19に対する分子状水素の補助的アプローチ：炎症制御と治療標的の検討


## Abstract

COVID-19, caused by SARS-CoV-2, is characterized by an exaggerated inflammatory response in which cytokine storms drive disease severity. This review examines the pathophysiological mechanisms underlying COVID-19 and surveys existing evidence showing that molecular hydrogen suppresses excessive inflammatory cells and mediators across a range of critical illnesses. In China, inhalation of a hydrogen-oxygen mixed gas was investigated as an adjunctive intervention for COVID-19 patients and was subsequently incorporated into national clinical guidelines. The review further evaluates the biological plausibility of hydrogen as an adjunct for COVID-19, identifying potential mechanistic targets including oxidative stress, inflammatory signaling, and immune dysregulation, and discusses the feasibility of hydrogen-based strategies in this context.

### Mechanism

Molecular hydrogen is proposed to selectively scavenge reactive oxygen species and suppress excessive pro-inflammatory cytokines, thereby attenuating the cytokine storm central to COVID-19 pathophysiology.

## Bibliographic

- **Authors**: Li Y, Wang Z, Lian N, Wang Y, Zheng W, Xie K
- **Journal**: Front Med (Lausanne)
- **Year**: 2021
- **PMID**: [34746162](https://pubmed.ncbi.nlm.nih.gov/34746162/)
- **DOI**: [10.3389/fmed.2021.671215](https://doi.org/10.3389/fmed.2021.671215)
- **PMC**: [PMC8569706](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8569706/)
- **Study type**: review
- **Delivery route**: inhalation
- **Effect reported**: not assessed

## Delivery context

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

## Safety notes

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)
- [LFL / UFL terminology](https://h2-papers.org/en/safety-notes/lfl-ufl-explained)
- [Inhalation safety threshold lineage](https://h2-papers.org/en/safety-notes/lineage)

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> **Cite as**: H2 Papers — PMID 34746162. https://h2-papers.org/en/papers/34746162
> **Source**: PubMed PMID [34746162](https://pubmed.ncbi.nlm.nih.gov/34746162/)