This study examined the effect of hot-spring bathing (40 to 41°C) on salivary secretion and salivary secretory IgA (sIgA) in healthy volunteers. Ten volunteers (10 men, average 33.6±9.3 years old) bathed in a hot-spring for 10 minutes.
Saliva samples were collected before bathing, during bathing (from 5 to 7 min), and after bathing using the Saxon test. The saliva flow rates and sIgA concentration were determined and then the sIgA secretion rates were calculated.
The saliva flow rates increased significantly during the bathing (p<0.02) and decreased after bathing. The sIgA secretion rates during bathing were significantly higher than those before and after bathing (p<0.02).
The increases in saliva flow rates and sIgA secretion rates during bathing were considered to indicate the improvement of local immunity in the oral cavity and thus considered to be useful for preventing upper respiratory tract infections.

Background: Nasal obstruction is an annoying condition. In this study, we evaluated the effects of hot spring bathing at 41 to 42°C using a rhinomanometer. Methods: Ten healthy adult volunteers (10 men, mean age of 27.8±4.4 years) were asked to bathe in a hot spring for 10 minutes. Using a rhinomanometer (HI-801), nasal resistance was measured before and after bathing by active anterior rhinomanometry. Total nasal resistance was calculated using Ohm’s law formula with right and left nasal resistance values (1/T=1/R+1/L, T: bilateral resistance, R: right resistance, L: left resistance). Resistance at ΔP=100 Pa was used for evaluation. Results: Right and left nasal resistance values were significantly decreased after bathing in subjects with a pre-bathing nasal resistance of greater than 0.75 Pa/cm3/s (inspiratory, P=0.0117; expiratory, P=0.0277; Wilcoxon t-test). No significant change was observed in subjects with a pre-bathing nasal resistance of below 0.75 Pa/cm3/s.Post-bathing total nasal resistance was significantly decreased in subjects with a pre-bathing nasal resistance of greater than 0.5 Pa/cm3/s (P=0.0115; Wilcoxon t-test). Conclusion: This study showed that nasal obstruction can be improved by hot spring bathing, which may contribute to the reasons why cold symptoms are relieved by hot spring bathing.