Purpose
 Electrodermal activity (EDA) is well known to be influenced by sympathetic activity. Although spa bathing alters autonomic nervous function, the effects of spa bathing on EDA have not been determined. We therefore examined the influence of spa bathng on EDA and autonomic nervous function.
Method
 When a gold electrode in test solution and another electrode on the palm were connected to a voltmeter and the index finger was inserted into the test solution, the maximum change of potential shown on the voltmeter was considered as EDA. Several kinds of spa water, tap water, refined water and alkaline ion water were used as test solutions. Electric conductivity, pH, oxidation reduction potential (ORP) and temperature were also measured. Five adult women participated in these tests.
To examine influences on the autonomic nervous system, Fourier analysis of the RR interval of heart rate was perforrned for three volunteers using electrocardiography before and after bathing in sulfur spa or tap water.
Results
 EDA displayed an extremely positive correlation to ORP, a weak negative correlation to pH and barely any relationship to electric conductivity of test solutions. Spectrum density at 0.04-0.15 Hz under Fourier analysis (LF) increased after sulfur bathing, but decreased after tap water bathing.
Discussion and conclusion : As EDA strongly correlated to ORP of solutions, epidermal cells may generate electric potential by extracellular ORP which may also produce intracellular electric potential altering membrane potential and consequently autonomic nervous functions might be influenced by the changed EDA.
 Since LF is consider to mainly comprise a parasympathetic component in resting state, the results of LF may indicate that the balance of autonomic nervous activity of the heart becomes more parasympathetic dominant after sulfur bathing and more sympathetic dominant after tap water bathing.
From above mentioned, bathing may have an electric influence on the human body by the ORP of bathing water.