Heat-retention effects of hydrogen-rich water bath assessed by thermography for humans
Kato S, Takada Y, Miwa N. · Journal of Thermal Biology. 2021;95:102805.
Study at a glance
In a 24-person bath study, some skin areas stayed warmer for an hour after hydrogen-containing baths. An axillary/core-temperature benefit was not shown. The experiment did not test treatment of illness or measure whole-body blood flow.
Human
Twenty-four healthy adults aged 24–58; eleven men and thirteen women. A selected subgroup had clearly visible capillaries.
LitaLife Ver.2 (WCJ, Osaka) electrolyzed 160 L tap water at 41°C for thirty or 120 minutes before a ten-minute neck-deep bath. Conditions at least seven days apart. Separate hand immersion used 15 L at 40°C for ten minutes. · After preparation, approximately 185 or 548 µg/L H₂ (not mg/L); ORP −91 or −167 mV. Thirty/120 minutes are water-preparation times, not body-exposure durations.
Ten-minute body bath; thermography before, immediately after, thirty and sixty minutes later. Separate ten-minute hand immersion, capillary measurements before and thirty/sixty minutes later.
Whole-body mean surface-temperature increases at sixty minutes were 0.65°C after thirty-minute preparation, 0.90°C after 120-minute preparation and 0.12°C control. Abdominal increases at thirty/sixty minutes: 1.82/1.96°C, 1.17/1.12°C and 0.44/0.66°C respectively. Some arm, upper-leg, hand and foot comparisons favored hydrogen. Selected capillary subgroup diameter increases at thirty/sixty minutes: 1.03/1.12 µm, 1.93/1.03 µm, versus −0.14/−0.59 µm control; authors report differences and 14.7–27.6% changes. Axillary temperature was nonsignificant; head/lower-leg heat retention was scarce or mixed. Higher concentration did not consistently yield greater regional effects. Body-composition correlations were not clearly stronger than control; basal-metabolic-rate correlation was negligible.
Small healthy sample, short surrogate outcomes, unstated randomized order, selected subgroup, many region/time comparisons without stated multiplicity adjustment. Diameter is not direct whole-body blood flow. Unequal bathrobe coverage and electrolysis-related changes in water chemistry complicate interpretation; proposed mechanisms remain speculative.
What kind of evidence is this?
Human
Within-person three-condition bath comparison, described as double-blind handled with dummy apparatus and coded/shuffled analysis. Randomized condition order not reported.
Musculoskeletal and pain research
Other forms
Information not yet classified
Some editorial classification fields are still pending. The source-reported outcomes and result are shown below; Hydrogenology does not infer a positive or negative signal from prose automatically.
Methods
Twenty-four healthy adults aged 24–58; eleven men and thirteen women. A selected subgroup had clearly visible capillaries.
24 in thermography. Capillary subgroup sixteen of 24; Figure 10 also labels n = 10, apparently measurement points but ambiguous. These are not separate groups of 24 or ten independent capillary patients.
Ten-minute body bath; thermography before, immediately after, thirty and sixty minutes later. Separate ten-minute hand immersion, capillary measurements before and thirty/sixty minutes later.
LitaLife Ver.2 (WCJ, Osaka) electrolyzed 160 L tap water at 41°C for thirty or 120 minutes before a ten-minute neck-deep bath. Conditions at least seven days apart. Separate hand immersion used 15 L at 40°C for ten minutes.
Hydrogen-containing topical water
After preparation, approximately 185 or 548 µg/L H₂ (not mg/L); ORP −91 or −167 mV. Thirty/120 minutes are water-preparation times, not body-exposure durations.
Same 41°C tap-water bath for ten minutes, approximately 0.8–1 µg/L H₂, ORP +479 mV; dummy apparatus.
Outcomes and reported result
Regional surface thermography, axillary temperature and selected finger-capillary loop diameters; correlations with body composition.
Whole-body mean surface-temperature increases at sixty minutes were 0.65°C after thirty-minute preparation, 0.90°C after 120-minute preparation and 0.12°C control. Abdominal increases at thirty/sixty minutes: 1.82/1.96°C, 1.17/1.12°C and 0.44/0.66°C respectively. Some arm, upper-leg, hand and foot comparisons favored hydrogen. Selected capillary subgroup diameter increases at thirty/sixty minutes: 1.03/1.12 µm, 1.93/1.03 µm, versus −0.14/−0.59 µm control; authors report differences and 14.7–27.6% changes. Axillary temperature was nonsignificant; head/lower-leg heat retention was scarce or mixed. Higher concentration did not consistently yield greater regional effects. Body-composition correlations were not clearly stronger than control; basal-metabolic-rate correlation was negligible.
Main-text methods, results, limitations and declarations were reviewed. Source versions, missing information and conflicting findings are stated in this record.
No systematic adverse-event assessment or counts stated; safety is not established by absent reporting.
A reported association, difference or mechanism is not automatically a clinical benefit.
Limitations and applicability
Small healthy sample, short surrogate outcomes, unstated randomized order, selected subgroup, many region/time comparisons without stated multiplicity adjustment. Diameter is not direct whole-body blood flow. Unequal bathrobe coverage and electrolysis-related changes in water chemistry complicate interpretation; proposed mechanisms remain speculative.
Limited to the population/model and protocol described above. These findings do not provide a treatment, concentration or device recommendation.
Japanese Center for Anti-Aging Medical Sciences grant 17T01 to Shinya Kato.
Authors declare no conflicts. The commercial device is identified; hosting by a retailer is not independent validation.
No single-study GRADE certainty rating is assigned. Read how records and evidence assessments are prepared.
Sources and record status
PMID: 33454037 · DOI: 10.1016/j.jtherbio.2020.102805
Complete final eleven-page Journal of Thermal Biology article, 95 (2021), 102805; online 5 December 2020. The copy is on a CDN linked by the research page of a Russian hydrogen-equipment retailer.
AI-assisted editorial review of the available main full text, 29 October 2026. No independent clinical or statistical assessment has been performed.
All eleven pages: Methods 2.1–2.5.1; Table 1; Results 3.1–3.4; Figures 1–10; Discussion; funding; conflicts and references.
AI-assisted editorial review of the available main full text, 29 October 2026. Complete final eleven-page Journal of Thermal Biology article, 95 (2021), 102805; online 5 December 2020. The copy is on a CDN linked by the research page of a Russian hydrogen-equipment retailer.
Ethics JCAAMS 17T01; no trial-registration identifier reported.
29 October 2026
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