Table 5. Representative research results of skin hydration measurement devices.

Study	Measurement location	Device	Principle	Correlation coefficient
Fluhr et al. (1999)10	Ventral forearm	Corneometer CM820	Capacitance	CM820/CM825 SCC: 0.8901
	Dorsal forearm	Corneometer CM825	Capacitance	CM820/Skicon 200 SCC: 0.8996
	Dorsal hand	Skicon 200	Conductance	CM820/Nova DPM SCC: 0.8165
	Front	Nova DPM	Impedance	CM820/DermaLab SCC: 0.8760
	Cheek	DermaLab	Conductance	CM825/Skicon 200 SCC: 0.8927
	Back (C4)			CM825/Nova DPM SCC: 0.7928
	Leg			CM825/DermaLab SCC: 0.8964
				Skicon 200/Nova DPM SCC: 0.8719
				Skicon 200/DermaLab SCC: 0.9358
				Nova DPM/DermaLab SCC: 0.8876
Alanen et al. (2004)19	Ventral forearm	Corneometer CM820	Capacitance	CM820/SC-2 SCC: 0.75 (Ventral forearm)
		MoistureMeter SC-2	Capacitance
Clarys et al. (2012)8	Sole of foot	Corneometer CM825	Capacitance	CM825/Skicon 200 PCC: 0.97
	Calf	Skicon 200	Conductance
	Knee
	Upper leg
	Palm
	Dorsal hand
	Ventral forearm
	Dorsal forearm
	Upper arm
	Forehead
	Cheek
	Abdomen
Hua et al. (2017)21	Face	Corneometer CM825	Capacitance	CM825/HP PCC: 0.808
	Forearm	HP	Conductance
Westermann et al. (2020)20	Forearm	Corneometer CM825	Capacitance	CM825/SkinUP PCC: 0.804 (Forearm)
	Forehead	SkinUp	Impedance	CM825/SkinUP PCC: 0.730 (Forehead)
	Cheeks			CM825/SkinUP PCC: 0.696 (Cheeks)
Choi et al. (2021)12	Ventral forearm	HP	Conductance	HP/Biodisplay PCC: 0.601 (Ventral forearm)
		Biodisplay	Capacitance
Present study	Ventral forearm	Corneometer CM820	Capacitance	CM820/HP PCC: 0.72 (Ventral forearm)
	Dorsal forearm	HP	Conductance	CM820/HP PCC: 0.74 (Dorsal forearm)
	Shin			CM820/HP PCC: 0.75 (Shin)
				CM820/HP PCC: 0.74 (Entire arm)
				CM820/HP PCC: 0.75 (Entire body)

SCC: Spearman’s correlation coefficient, HP: hydration probe, PCC: Pearson’s correlation coefficient.