Commentary

Update on green tea


 

References

During the last 25 years, green tea, which is derived from Camellia sinensis (an evergreen member of the Theaceae family), has gained considerable attention because of its purported antioxidant and anticarcinogenic properties. Believed to have been used by human beings for 4,000 years,1 green tea is now one of the most heavily researched of the antioxidants, with numerous studies of its cutaneous effects appearing in the literature.2 Laden with plant polyphenols, orally administered or topically applied green tea has been shown to display significant antioxidant, chemopreventive, immunomodulatory, and anti-inflammatory activity, affecting the biochemical pathways important in cell proliferation.3-6 For this reason, and due to its global popularity as a beverage, green tea polyphenols are among the most frequently studied herbal agents used in medicine.

Polyphenols, many of which are potent antioxidants, are a large diverse family of thousands of chemical compounds present in plants. The four major polyphenolic catechins present in green tea include: ECG [(-)EpiCatechin-3-O-Gallate], GCG [(-)GalloCatechin-3-O-Gallate], EGC [(-)EpiGalloCatechin], and EGCG [(-)EpiGalloCatechin-3-O-Gallate], the most abundant and biologically active green tea constituent. In fact, EGCG is the component associated with the greatest anticarcinogenic and chemopreventive properties.6

Dr. Leslie S. Baumann

Dr. Leslie S. Baumann

A wide-ranging evidence-based review of the use of botanicals in dermatology, published in 2010, showed that the oral administration, in particular, as well as topical application of antioxidant plant extracts of green tea, among other botanicals, can protect skin against the harmful effects of UV exposure, including erythema, premature aging, and cancer.7

Green tea is thought to be challenging to formulate because of the inherent hydrophilicity of EGCG, which limits penetration into human skin.8,9 Nevertheless, green tea is thought to have great potential in traditional sunscreens to enhance photoprotection.10,11 The photoprotective activity of orally administered or topically applied green tea has been supported in various studies.12-15

The remainder of this column will focus on recent studies of topically applied green tea polyphenols in human beings as well as clinical uses of this agent.

Topical uses

Topical green tea appears to reduce skin inflammation and neutralize free radicals, which explains its popularity as an additive in rosacea and antiaging skin care products. The antiaging effects of green tea are difficult to measure because it functions as an antioxidant that prevents aging and does not have the capacity to increase collagen synthesis or ameliorate already existing wrinkles. However, there is relatively good evidence, in comparison to other antioxidants, suggesting that topically applied green tea can help protect skin from UV radiation.16

Investigators performed a thorough literature search of all in vitro, in vivo, and controlled clinical trials involving green tea formulations and their dermatologic applications, which was published in 2012. They evaluated 20 studies, with evidence suggesting that orally administered green tea displays a broad range of healthy activity, and supportive data for the use of topically applied green tea extract for treatment of various cutaneous conditions, including acne, rosacea, atopic dermatitis, androgenetic alopecia, hirsutism, candidiasis, keloids, leishmaniasis, and genital warts.17

Also, a green tea topical formulation, green tea sinecatechin Polyphenon E (Veregen) ointment, has recently been shown to exert antioxidant, antiviral, and antitumor activity, and has demonstrated efficacy in treating Condylomata acuminata (external anogenital warts).18 In addition, topically applying green tea catechins in the morning in combination with traditional sunscreens is believed to have the potential to protect the skin from UV-induced damage. Topical green tea may improve rosacea, prevent retinoid dermatitis, and play a role in managing pigmentation disorders. Few of the many over-the-counter products that contain green tea catechins have been tested in controlled clinical trials and the concentration of polyphenols in these products is too low to demonstrate efficacy. It is necessary to know the amount of green tea catechins in a formulation to judge its efficacy.

Acne

In 2009, in a 6-week study investigating the efficacy of 2% green tea lotion for the treatment of mild-to-moderate acne vulgaris in 20 patients, researchers reported statistically significant reductions in mean total lesion count and mean severity index (devised by the authors to correlate with total lesion count in increasing intensity, scaled from 1 to 3). They concluded that 2% green tea lotion is both an effective and cost effective approach for treating mild-to-moderate acne lesions.19

A 2012 study revealed that ethanol extracts of several herbs, including green tea, exhibited the potential for inhibiting acne when incorporated into a topical moisturizer, specifically acting against acne-causing bacteria without provoking irritation.20 Earlier that year, other investigators conducted in vitro and in vivo experiments to evaluate the effects against acne of polyphenon-60, which contains various green tea catechins (now referred to as sinecatechins in the United States.).21 In this clinical study, patients exhibited improvement in acne symptoms, including a reduction in the number of pustules and comedones.22

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