Several environmental and genetic factors are involved in skin cancer induction, however exposure to chemical carcinogens and solar ultraviolet (UV) radiation are primarily responsible for several skin diseases including skin cancer. Chronic exposure of solar UV radiation to the skin leads to basal cell and squamous cell carcinoma, and melanoma. Chemoprevention of skin cancer by consumption of naturally occurring botanicals appears a practical approach and therefore world-wide interest is considerably increasing to use these botanicals. Sunscreens are useful but their protection is not ideal because of inadequate use, incomplete spectral protection and toxicity. Silymarin, a plant flavonoid isolated from the seeds of milk thistle (Silybum marianum), has been shown to have chemopreventive effects against chemical carcinogenesis as well as photocarcinogenesis in various animal tumor models. Topical treatment of silymarin inhibited 7,12-dimethylbenz(a)anthracene-initiated and several tumor promoters, like 12-O-tetradecanoylphorbol-13-acetate, mezerein, benzoyal peroxide and okadaic acid, induced skin carcinogenesis in mouse models. Similarly, silymarin also prevented UVB-induced skin carcinogenesis. Wide range of in vivo mechanistic studies indicated that silymarin possesses antioxidant, anti-inflammatory and immunomodulatory properties which may lead to the prevention of skin cancer in in vivo animal models. The available experimental information suggests that silymarin is a promising chemopreventive and pharmacologically safe agent which can be exploited or tested against skin cancer in human system. Moreover, silymarin may favorably supplement sunscreen protection and provide additional anti-photocarcinogenic protection.

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