Disclosed is a method with different exemplary embodiments for determining a degree of damage to hair. Said method can comprise the following steps: during the exposure of a hair sample to near-infrared and/or infrared light, recording a spectrum of at least part of the near-infrared and/or infrared light that has interacted with the hair sample, comparing at least part of the spectrum with a spectroscopic calibration model obtained by near-infrared and/or infrared spectra and degrees of damage of a plurality of calibration hair samples, and determining the degree of damage to the hair using said comparison.