We have investigated depth-resolved cellular structures of unmodified fresh 
human scalp hairs with ultrahigh-resolution full-field optical coherence 
tomography (FF-OCT). The Linnik-type white light interference microscope has 
been home-implemented to observe the micro-internal layers of human hairs in 
their natural environment. In hair shafts, FF-OCT has qualitatively revealed the 
cellular hair compartments of cuticle and cortex layers involved in keratin 
filaments and melanin granules. No significant difference between black and 
white hair shafts was observed except for absence of only the melanin granules 
in the white hair, reflecting that the density of the melanin granules directly 
affects the hair color. Anatomical description of plucked hair bulbs was also 
obtained with the FF-OCT in three-dimensions. We expect this approach will be 
useful for evaluating cellular alteration of natural hairs on cosmetic 
assessment or diagnosis of hair diseases.