Topical isoflavones provide effective photoprotection to skin

Summary Background/purpose: Isoflavones, one main group of phytoestrogens, have antioxidative and photoprotective effects in cellular and mouse studies. The aim of this study is to obtain a more comprehensive understanding of the isoflavone‐mediated photoprotection with the pig skin model, a more human‐resembling model. Methods: The pig skin was treated with five well‐known isoflavone compounds (genistein, equol, daidzein, biochanin A, and formononetin) and one antioxidant combination solution of 15% vitamin C and 1% vitamin E and 0.5% ferulic acid (CEF) daily for 4 days. Skin was irradiated with solar‐simulated UV irradiation, 1 to 5 minimal erythema dose (MED) at 1‐MED intervals. Evaluation was carried out 24 h later by colorimeter‐measured erythema and sunburn cell numbers. Results: Topical application of 0.5% solutions of three individual phytoestrogens – genistein, daidzein, biochanin A – are better than similar solutions of equol or formononetin in protecting pig skin from solar‐simulated ultraviolet (SSUV)‐induced photodamage, as measured by sunburn cell formation and/or erythema. However, the protection was less than that provided by a topical combination antioxidant standard containing 15% L‐ascorbic acid, 1%α‐tocopherol, and 0.5% ferulic acid. Conclusion: Isoflavones provide effective photoprotection and are good candidate ingredients for protection against ultraviolet (UV) photodamage.