New insights on dandruff/seborrhoeic dermatitis: the role of the scalp follicular infundibulum in effective treatment strategies.

Pathogenesis of dandruff/seborrhoeic dermatitis (D/SD) involves Malassezia yeasts, leading to the most widely accepted treatment strategy of topical application of antifungal agents, usually from rinse-off shampoos. The scalp spatial distribution of Malassezia must be mirrored by the distribution of the active agent to realize the full benefit of the active material. Based on observations that Malassezia yeasts reside in follicular infundibula, we sought to determine whether commercial shampoo products based on the active agent zinc pyrithione (ZPT) could deliver this material to this highly restricted, but therapeutically relevant space. Three new methods have been developed to assess ZPT active delivery to the follicular infundibulum: (i) hair plucks followed by chemical quantification of the subsurface portion; (ii) cyanoacrylate infundibular biopsies followed by chemical quantification of extracted ZPT; and (iii) confocal microscopy of infundibular spaces coupled with image analysis to yield relative quantification. Infundibular ZPT was detected, the quantity of which directly correlated with the consequent reduction of the infundibular Malassezia population. A commercial therapeutic shampoo delivered a disproportionately high level of ZPT to the infundibular spaces, suggesting an active mechanism to draw ZPT particles of optimum size to this space. Imaging of the infundibular ZPT in vivo allows an assessment of its state of aggregation, which would tend to minimize bioavailability. Effective therapeutic D/SD products must deliver the antifungal active material to the infundibulum as well as superficially on the scalp surface. This is achieved by certain therapeutic ZPT shampoos, in which the particle size of ZPT is likely to be an important factor in determining the efficiency of spatial delivery.