# Inhaled hydrogen gas therapy for prevention of noise-induced hearing loss through reducing reactive oxygen species.
> 水素ガス吸入による騒音性難聴の予防：活性酸素種の低減を介した内耳保護効果


## Abstract

Reactive oxygen species (ROS) generated in the inner ear are central to the development of noise-induced hearing loss (NIHL). This animal study investigated whether H2 gas inhalation could mitigate NIHL in guinea pigs exposed to noise, followed by daily 5-hour inhalation of 0.5%, 1.0%, or 1.5% H2 for five consecutive days. Auditory brainstem response measurements showed that threshold shifts improved significantly in the 1.0% and 1.5% H2 groups relative to untreated controls. Outer hair cell (OHC) survival assessed 7 days post-exposure was markedly higher in the 1.0% and 1.5% groups, particularly in the basal cochlear turn. Immunohistochemical staining for 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, revealed substantially reduced immunoreactivity in H2-inhaled animals compared with controls. These findings indicate that H2 inhalation at concentrations of 1.0% and above confers meaningful protection against noise-induced cochlear injury through ROS suppression.

### Mechanism

Inhaled H2 selectively scavenges ROS produced in the inner ear following noise exposure, reducing oxidative DNA damage (measured by 8-OHdG immunoreactivity) in outer hair cells and thereby limiting cochlear injury.

## Bibliographic

- **Authors**: Kurioka T, Matsunobu T, Satoh Y, Niwa K, Shiotani A
- **Journal**: Neurosci Res
- **Year**: 2014
- **PMID**: [25196919](https://pubmed.ncbi.nlm.nih.gov/25196919/)
- **DOI**: [10.1016/j.neures.2014.08.009](https://doi.org/10.1016/j.neures.2014.08.009)
- **Study type**: animal study
- **Delivery route**: inhalation
- **Effect reported**: positive
- **H2 concentration**: 0.5–1.5%

## 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 25196919. https://h2-papers.org/en/papers/25196919
> **Source**: PubMed PMID [25196919](https://pubmed.ncbi.nlm.nih.gov/25196919/)