A method and a device for determining a degree of thermal hair damage are provided. A method for determining a degree of thermal hair damage includes, during exposure of a hair sample of hair to UV or UV/VIS light, recording a spectrum of at least a portion of the UV or UV/VIS light that has interacted with the hair sample. Further, the method includes comparing at least a portion of the spectrum with a spectroscopic calibration model obtained using UV or UV/VIS spectra and degrees of thermal damage of a plurality of calibration hair samples. Also, the method includes determining the degree of thermal hair damage by using the comparison.
