A measurement system for light-based measurement of collagen, using a first light intensity and a second light intensity according to the invention, compromises a light source (120) for emitting a light beam having a source wavelength range and an optical system (130) to polarize light within the source wavelength range, thereby generating a polarized light beam (140), and to direct and focus the polarized light beam (140) to a target position inside the skin (160) at a predetermined focus depth below an outer surface of the skin. The measurement system further comprises a first detector (150) and a second detector