The invention provides a hair treatment device (40) comprising a light-based detector (10) for detecting a hair (22) near a skin surface (21) and a method for detecting a hair (22) near a skin surface (21). The detector (10) comprises a light source (11), optical elements (14, 16, 17, 18) and a polarization-sensitive light sensor (12, 13). The light source (11) generates a light beam (31) and the optical elements (14, 16, 17, 18) focus the light beam (31) at a hair (22) near the skin surface (21). The polarization-sensitive light sensor (12, 13) is provided for detecting light interacted with the hair (22) or the skin surface (21) and having a predefined linear polarization. The light source (11) and/or the optical elements (14, 16, 17, 8) are arranged to cause the light beam (31), when reaching the skin surface (21), to have a polarization direction which is time-invariant and spatially variant in cross-sections of the 10 light beam.
