# Heat-retention effects of hydrogen-rich water bath assessed by thermography for humans.
> サーモグラフィを用いた水素富化水浴の保温効果に関する臨床的検討


## Abstract

A thermographic clinical trial involving 24 healthy participants compared heat retention after hydrogen-rich water bathing (hydrogen concentration 185–548 μg/L; oxidation-reduction potential −167 to −91 mV) versus ordinary water bathing under identical conditions (41°C, 10 minutes). Infrared imaging at 30 and 60 minutes post-bath revealed greater surface temperature maintenance in the hydrogen-rich group across multiple body regions, ranked in descending order: abdomen, upper legs, arms, hands, and feet. Fingertip capillary thickness measurements indicated vascular dilation was more pronounced after hydrogen-rich bathing, pointing to a circulatory-promoting effect beyond simple thermal retention. Heat retention showed weak-to-moderate positive correlations with subcutaneous fat, total body fat, and BMI, and an inverse correlation with skeletal muscle ratio, while basal metabolic rate showed little association. These findings suggest hydrogen-rich water bathing enhances post-bath warmth across diverse body regions through blood flow promotion reflected by capillary expansion.

### Mechanism

Hydrogen-rich water bathing appears to dilate peripheral capillaries and enhance blood circulation, producing post-bath heat retention that exceeds what thermal effects alone would predict.

## Bibliographic

- **Authors**: Kato S, Takada Y, Miwa N
- **Journal**: J Therm Biol
- **Year**: 2021
- **PMID**: [33454037](https://pubmed.ncbi.nlm.nih.gov/33454037/)
- **DOI**: [10.1016/j.jtherbio.2020.102805](https://doi.org/10.1016/j.jtherbio.2020.102805)
- **Study type**: human observational study
- **Delivery route**: hydrogen bath
- **Effect reported**: positive

## Delivery context

Hydrogen bathing has reports of localized effects, but for systemic hydrogen intake the most efficient route is inhalation. Inhalation carries explosion risk (empirical LFL of 10%; high-concentration devices are documented in the Consumer Affairs Agency accident database and are not recommended).

## Safety notes

Hydrogen bathing has reports of localized effects, but for systemic hydrogen intake the most efficient route is inhalation. Inhalation carries explosion risk (empirical LFL of 10%; high-concentration devices are documented in the Consumer Affairs Agency accident 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)

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> **Cite as**: H2 Papers — PMID 33454037. https://h2-papers.org/en/papers/33454037
> **Source**: PubMed PMID [33454037](https://pubmed.ncbi.nlm.nih.gov/33454037/)