The present disclosure relates to a method and a device (10) for determining a hydration state of skin tissue. The device (10) comprises an interface (22) for receiving a data stream (100) comprising a plurality of PPG signals including at least a first PPG signal (104) indicative of a first wavelength range (72), a second PPG signal (106) indicative of a second wavelength range (74), and a third PPG signal (108) indicative of a third wavelength range (76), a processing unit (24) for computing at least a first combined signal (116) based on a first pair of signals (104, 106) selected from the plurality of PPG signals, and a second combined signal (118) based on a second pair of signals (108, 110) selected from the plurality of PPG signals, wherein at least one PPG signal of the second combined signal (118) is dependent on a tissue hydration level, and an analysis unit (26) for computing a hydration signal (34) indicative of skin hydration, wherein the hydration signal (34) is derived from the first combined signal (116) and the second combined signal (118).