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Why Sunscreens Do Not Fully Prevent Skin Cancer

June 2005

By Dale Kiefer

Licorice (Glycyrrhiza Glabra)

Licorice Extract and Rosemary

Licorice, derived from the roots of Glycyrrhiza glabra, has been used medicinally for more than 4,000 years. Modern science has confirmed that licorice is a powerful skin protectant. Numerous studies suggest that licorice extract protects the skin from the damaging effects of UV light.73,74 Licorice extract also has demonstrated efficacy in treating atopic dermatitis, an allergy-related, intensely itchy swelling of the skin.75

In animal studies, a preparation containing 0.5% glabridin, one of the primary active constituents in licorice extract, prevented the redness and inflammation normally associated with UV exposure when pre-applied to the skin. Licorice extract also reduces melanin synthesis.74 Recent research suggests that UV-induced DNA damage and subsequent repair efforts precede melanin synthesis.11 Furthermore, licorice extract’s antioxidant activity has been shown to enhance the stability of other compounds when added to a topical dermatological cream.76 This antioxidant activity evidently protects skin against damage caused by free radical and reactive oxygen species.73

Rosemary (Rosmarinus officinalis), a fragrant evergreen perennial herb, has been used as a seasoning and medicinal herb for several millennia. Rosemary contains numerous beneficial compounds, including cancer-fighting chemicals, antioxidants, and anti-inflammatory agents.77-79 At least two of these, carnosic acid and ursolic acid, are especially beneficial to skin.80-82 Application of rosemary extract has been shown to prevent chemically induced skin tumors in a mouse model of human skin cancer. Depending on the concentration of the extract, tumors were inhibited by up to 99%.80

Rosemary (Rosmarinus Officinalis)

Earlier this year, French researchers demonstrated that ursolic acid, derived from rosemary, significantly inhibited the proliferation of melanoma cells in culture, apparently by promoting apoptosis (programmed cell death).82 More than a decade earlier, Rutgers University scientists demonstrated that in a mouse model of human skin cancer, both carnosic and ursolic acids markedly inhibit tumor growth when applied to the skin.80 Korean scientists have shown that “ursolic acid significantly suppressed the UVA-induced reactive oxygen species production and lipid peroxidation” in a human keratinocyte culture. They concluded that ursolic acid “may be useful in the prevention of UVA-induced photoaging.”83 In addition, research has demonstrated that when specially formulated with lipids, ursolic acid enhances the dermal collagen and ceramide content of normal human epidermal keratinocytes.84,85 Collagen provides the “skeleton” that gives shape and structure to the skin, while ceramide is a lipid that helps maintain proper immune function, as well as youthful moisture content, in the skin. Keratinocytes make up as much as 95% of epidermal tissues and are responsible for producing keratin, the tough protein that contributes to healthy hair, nails, and skin.


When it comes to protecting yourself against skin cancer, the most common of cancers worldwide, sunscreen agents such as zinc oxide alone may not be enough. While sunscreens can help shield against UV light-induced sunburn, it is crucial to also protect the skin against the free radicals generated by solar radiation. Left unchecked, these notoriously harmful agents may contribute to skin aging, DNA damage, and skin cancer.

Fortunately, a number of powerful plant-derived phytochemicals may help protect the skin via novel mechanisms that are distinct from those provided by sunscreen agents. Emerging evidence suggests that topically applied botanicals—including green tea, milk thistle, grape seed, turmeric root, licorice root, and rosemary—may prevent deleterious effects from sun exposure such as inflammation, DNA damage, immune deficits, skin aging, and cancer. The potent antioxidant properties of these plant extracts may account for their skin-protective actions.

The combination of sunscreen agents with botanical extracts may thus provide the most complete protection against the harmful effects of UV light, by both screening solar rays and preventing the formation of damaging free radicals. These combinations offer promise not only in helping to guard against skin cancers but also in promoting healthy, youthful skin.


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