Daidzein is an isoflavone found naturally in legumes such as soybeans, alfalfa and red clover (R). A phytoestrogen, it is metabolised in soybeans to produce compounds that act as defense mechanisms against pathogens (R).
Daidzein is more hydrophilic than genistein, which may explain its generally lower skin absorption. The pH of the formulation significantly affects its skin deposition, which was higher at pH 6 compared to pH 10.8 in the skin of mice and pigs. Interestingly, the skin uptake of daidzein surpassed that of genistein when an aglycone mixture was used as the active ingredient (R). The loading of daidzein on to nanostructured lipid carriers has also been shown to improve its delivery across rat skin (R).