Several aspects of the intermediate filaments' molecular architecture remain 
mysterious despite decades of study. The growth process and the final 
architecture may depend on the physical, chemical, and biochemical environment. 
Aiming at clarifying this issue, we have revisited the structure of the human 
hair follicle by means of X-ray microdiffraction. We conclude that the 
histology-based growth zones along the follicle are correlated to the fine 
architecture of the filaments deduced from X-ray microdiffraction. Our analysis 
reveals the existence of two major polymorph intermediate filament 
architectures. Just above the bulb, the filaments are characterized by a 
diameter of 100 Angstroms and a low-density core. The following zone upwards is 
characterized by the lateral aggregation of the filaments into a compact network 
of filaments, by a contraction of their diameter (to 75 Angstroms) and by the 
setting up of a long-range longitudinal ordering. In the upper zone, the small 
structural change associated with the tissue hardening likely concerns the 
terminal domains. The architecture of the intermediate filament in the upper 
zones could be specific to hard alpha-keratin whilst the other architecture 
found in the lower zone could be representative for intermediate filaments in a 
different environment.