ABSTRACT
The most important interactions of hair cosmeceutical products occur at the hair fiber surface, in the first few layers of the cuticle, and in the cortex of damaged hair. While laws and regulations impose more constraints on the cosmetic scientist and manufacturer now than ever before, it is important that practitioners be equipped to recommend or dissuade patients from incorporating a cosmeceutical into their regimen. The same characteristics that make a cosmeceutical attractive for the skin are sought after in hair and nail formulations. Made of very thin, flat cells reminiscent of fish scales, the cuticle's main function is protection of the underlying cortex and anchoring the follicle in place. The majority of hair fiber mass is attributable to the cortex. Unlike cells of the external cuticle, those of the cortex are thin, long, and longitudinally oriented parallel to the axis of the hair. Interdigitation of cortical cells confers mechanical strength to the hair shaft.
