The existence of a thin chemically resistant layer, the epicuticle, close to the surfaces of all undamaged mammalian keratin fibres has been known since 1916. The identification of such a specific structure within the fibre cuticle has remained elusive. Now, through transmission electron microscope investigations of stained transverse sections of hairs from various animal species, the epicuticle has been tentatively identified as a sharply defined and continuous layer approximately 13 nm thick covering the entire outwardly facing intracellular surface of every cuticle cell. The staining behaviour of the epicuticle leads one to suppose that it is rich in cystine and that thioester‐bound lipids might be present within its bulk. With the atomic force microscope it was established that the undamaged outer surface of all mammalian keratin fibres, even including those from the monotremes, were longitudinally striated. The lateral spacing of the striations was always in the range 0.29–0.39 µm. Striations only occurred on the freely exposed outer surfaces of the original undamaged fibres; evidently arising by some, as yet undefined, interaction in the follicle with the cuticle of the inner root sheath. By stripping off fatty acids known to be covalently attached to the fibre's outer surface, the striations were shown to reflect a corresponding irregularity of the epicuticle's surface.

S Y N O P S I SWhen thin sections of human hair are treated with a solution containing silver nitrate and hexamethylene tetramine (Gomori's silver-methenamine reagent) under alkaline conditions not only does morphological staining of the sections occur but with increasing time of treatment metallic silver particles are also produced in the sections. It is shown that these particles are the results of the interaction of the reagent with cystine.The metal-precipitation technique was used to determine the location and distribution of cystine in Caucasian human hair.

Synopsis Some previously unreported fine variations in the form of normal hairs are described as they are observed in the scanning electron microscope (SEM). They all arise in the course of surface frictional wear and the chipping away of the hair surface scale edges and include remanent surface impressions of cuticle scale edges, 'false' scale edges, granular surface remnants and highly irregular (chevron) scale patterns. Mechanisms are proposed for the way in which each of these different fine features arise. The paper also contains deliberations on the conditions for operating the SEM consistent with obtaining the best information about the architecture of hair surfaces. The correctness of viewing orientation of scanning electron micrographs is also emphasized to avoid misinterpretation of features on the hair surface.

Summary:The atomic force microscope (AFM) was used to investigate the surface architecture of the entire lengths of cleaned human head hairs. Many features previously seen with the scanning electron microscope (SEM) were identified. However, the AFM has provided much greater detail and, in particular, the hair's cuticular surfaces appear not to be as smooth as had been previously supposed. A consistent feature was of step discontinuities or "ghosts" on the scale surfaces. These delineated the original location of each overlying scale before its edge had been chipped away. There was a change in the longitudinal angular presentation of the surfaces about each ghost. This means the distal ends of each cuticle cell have been synthesised in the follicle to be thicker than where that same cuticle cell is bounded on both sides by other cuticle cells. The undamaged outer cuticular surfaces at the root end of each hair were covered everywhere by longitudinal ridges (striations). Where the hair surface was worn, the striations terminated at a scale edge ghost. The ridges were approximately 9 nm high and were in parallel array with a lateral repeat spacing of about 350 nm. The striations are evidently formed on the outer surface of each cuticle cell following earlier contact in the hair follicle with the inner root sheath. The study of stained transverse sections of hairs in the transmission electron microscope (TEM) is suggested as a means for throwing some light on the underlying structure and chemistry of the striations. Finally, our AFM studies have revealed that the surface of the freshly emergent hair gradually changes over a distance of about 20 mm and that the surface of the hair for most of its length is quite different from that near the root. This is likely to be of import to those engaged in the hair toiletries industry.

Premature fracture and splitting of human head hair is cosmetically undesirable and at worse, unsightly. It is often regarded both by the hair's owner and by others as indicative of hair in poor condition and attracts considerable expenditure on hair toiletry products in sometimes vague attempts to prevent or repair the damage. This paper defines the mechanical events which underlie the fracture of hairs as they occur on the head and insofar as they satisfy the different fracture morphologies seen under the scanning electron microscope. Factors affecting propensity for fracture are considered. A significant conclusion is that hair 'strength', as might be assessed by the consumer, has little to do with the tensile mechanical properties of the fibres but that bending and associated longitudinal shear processes are of much greater relevance.