The present disclosure is concerned with a personal hygiene device (100), in particular a toothbrush, having a handle (140), a treatment head (120) mounted for relative movement of at least a portion of the treatment head (120) with respect to the handle (140) against a restoring force (160) when a treatment force is applied in at least one direction onto the treatment head (120), a treatment force measurement unit for determining the applied treatment force comprising a light emitting element (171), a light sensitive element (172), and a light changing element (180) arranged at least partly in the light path between the light emitting element (171) and the light sensitive element (172), wherein the light changing (180) element and at least one of the light emitting element (171) or light sensitive element (172) are arranged to be moved relatively to each other when at least the portion of the treatment head (120) is moved.
