Influence of the lipid-phase composition on the trans-epidermal transfer of vitamin B6 from O/W emulsions

Transfer of bioactives through epidermis can be viewed as a model of bioavailability for functional cosmetics and is relevant to their efficacy. Nine equivalent O/W emulsions differing in the composition of the lipid phase were comparatively tested for their ability to release vitamin B6 through 18-days-old reconstructed human epidermis, in vitro. Formulations afforded efficient diffusion of the vitamin through the skin, although the actual flux varied considerably, with coefficient of permeability in the range 15.0 – 297.3 10-5cm/h at 34°C. Bioavailability grew in the order: sesame oil < squalane ~ raw wheat germ oil < dibutyladipate ~ polydimethylsiloxane. Addition of 5% w/w free fatty acids (stearic, lauric, caprilyc, and oleic) to lowest performing sesame oil increased the bioavailability by 1.2-fold, 6-fold, 20-fold and 10-fold respectively.