Selective biodegradation in hair shafts derived from archaeological, forensic and experimental contexts.

BACKGROUND: Hair is degraded by the action of both dermatophytic and nondermatophytic microorganisms. The importance of understanding hair sample condition in archaeological and forensic investigation highlights the need for a detailed knowledge of the sequence of degradation in samples that have been either buried or left exposed at the ground surface.
OBJECTIVES: To investigate the sequence of biodegradative change to human terminal scalp hair from archaeological and forensic contexts.
METHODS: Cut modern scalp hair from three individuals with caucasoid-type hair was inoculated with soil microorganisms through soil burial in the field and under laboratory conditions to produce experimentally degraded samples. The degraded hair fibres were subjected to detailed histological examination using a combination of high-resolution light microscopy, transmission electron microscopy and scanning electron microscopy to investigate the nature and sequence of degradative change to hair structural components. RESULTS/DISCUSSION: Degradation was found to occur first within the least structurally robust components that afford the least resistance to microbial/chemical attack. The sequence of degradation (most to least-reflecting degree of vulnerability) in the hair cuticle was as follows: (1) intercellular delta-layer (cell membrane complex); (2) endocuticle; (3) cell membrane beta-layers; (4) exocuticle; (5) epicuticle; and (6) A-layer. In the hair cortex this was as follows: (I) intercellular delta-layer (cell membrane complex); (II) cell membrane beta-layers; (III) intermacrofibrillar matrix/nuclear remnants; (IV) microfibrils; (V) intermicrofibrillar matrix; and (VI) pigment granules (the hair fibre component that was the least vulnerable to degradation).
CONCLUSIONS: The selective progress of degradation in the hair shaft has been charted and this provides a basis for further histological work in better understanding the condition of hair fibres derived from archaeological or forensic contexts as well as being relevant to investigation of diseased hair, in particular hair infected by dermatophytes and hair weakened by genetic hair shaft abnormalities.