L4.      Degradation of the hair follicle inner root sheath.
Gill Westgate, *Steven Goff, *Paul Slusareewicz, *Preyesh Parmar; Westgate Consultancy, Stevington, Bedfordshire, *Life Science, Unilever R&D, Colworth, Sharnbrook, Bedford, UK.

A widely held belief in hair research is that degradation of the inner root sheath (IRS) is mediated by a function of the sebaceous gland. This belief has been supported by the fact that isolated human hair follicles lacking sebaceous glands grow fibres in culture to which the root sheaths appear to remain attached. Here we report that this is not the case. The fibres of follicles lacking sebaceous glands, when grown in culture, are encased in a layer of translucent tissue. During hair growth in vitro this tissue remains intact at the distal end of the follicle but appears to be absent further down towards the bulb. Transection within the region lacking this tissue results in the release of a naked hair fibre and the production of hair with no attached sheath tissue upon further growth. Additionally by utilising a serial sectioning technique we demonstrate that the translucent tissue does in fact represent the IRS and that this tissue is indeed degraded in vitro in the absence of the sebaceous gland. Finally by histological comparison with freshly isolated pilosebaceous units indicates that IRS degradation in vitro strongly resembles the process that occurs in vivo. Taken together these data suggest that current thoughts regarding the mechanism of IRS degradation is flawed and indicate that the sebaceous gland does not itself participate in this process. IRS degradation appears to be a function of the follicle itself and is probably intimately linked with the processes of cellular differentiation that occur during hair biogenesis. Furthermore these data further validate the human hair follicle culture model with respect to its ability to reproduce the processes of hair formation, which occur in vivo.