Transdermal absorption of phytoestrogens.

The transdermal absorption of the isoflavones, daidzein and genistein, applied on the skin in olive oil was studied in vivo. The concentrations of the isoflavones and their metabolites were monitored in plasma and urine by GC-MS methods. It was found that the concentration of genistein in plasma was 3-fold higher than the plasma concentration of daidzein. In contrast, daidzein excretion was 2-3-fold higher than that of genistein in urine. The excretion rate of the studied phytoestrogens in urine and their concentration in plasma was significantly decreased after repeated transdermal application. The urinary recovery of administered daidzein and genistein after the first application was 15.9% and 7.7%, respectively and this dropped to 1.6% and 0.7% after the second application. The results obtained might suggest that daidzein and genistein are captured in the skin following repeated transdermal application.