Do herbal tea, tea, and infusions have effects on the skin?

Teas and other herbal-based beverages are believed to have intriguing effects on the skin. However, the green tea is the drink with the most scientific evidence associated with skin benefits, particularly in the prevention of skin cancers.

Hasan MUKHTAR and his colleagues evaluated the protective effect of polyphenols isolated from green tea (organic molecules, GTP) on changes induced by UVB radiation in murine skin, particularly tumorigenesis. Oral administration of 0.2% GTP as a source of drinking water for 30 days to mice, followed by UVB irradiation, resulted in protection against skin edema and depletion of the antioxidant system in the epidermis. The administration of GTP also resulted in protection against the activity of cyclooxygenase, an enzyme overexpressed in cases of cancer. The induction of ornithine decarboxylase (ODC), a known marker of cell proliferation, is considered a specific manifestation of the tumor promotion process. The protective effect of GTP against the induction of ODC was also observed in this study.

Thus, researchers have observed a reduction in the markers of tumor promotion in murine skin, suggesting the chemopreventive effects associated with green tea. Cyclooxygenase is known to play a significant role in skin inflammation, cell proliferation, and the promotion of skin tumors. Arachidonic acid, released through the skin by stimuli, undergoes oxidative metabolism involving the cyclooxygenase pathway, leading to the formation of prostaglandins involved in inflammation. The significant increase in cyclooxygenase activity caused by UVB radiation in mouse skin suggests its correlation with the pro-oxidant state caused by UVB and, collectively, its role in promoting UVB-induced tumors.

The findings of this study suggest that green tea consumed orally, particularly the polyphenols it contains, may be beneficial in combating the promotion of sun-associated carcinogenesis.

Reema Gabrani and her team focused on exploring the antimicrobial activity of green tea aqueous extract on selected bacterial strains, by conducting a standard disk diffusion test. Staphylococcus epidermidis, Micrococcus luteus, Brevibacterium linens, Pseudomonas fluorescens and Bacillus subtilis were found to be sensitive to the green tea extract during the test (inhibition zone ≥ 7 mm). Furthermore, the effect of the aqueous extract on the adhesion of different bacteria to cells indicates that it inhibits adhesion to cells.

Although these bacteria are generally harmless to the skin, some like S. epidermis can cause skin infections such as atopic dermatitis. This study confirms the antimicrobial activity in vitro of green tea leaf extract against skin pathogens. The currently proposed mechanism of action is that green tea prevents the adhesion of bacterial pathogens to the surface membranes of host cells.

Nevertheless, in vivo experiments would confirm these results.

In a study led by Kazuo KONDO, the aim was to characterize the factors that influence age-associated hyperpigmentation, particularly the sources of dietary polyphenols found in green tea, for example. A cross-sectional survey was conducted among healthy Japanese women aged 30 to 60 years (n = 244) using dietary and environmental questionnaires and a facial analyzer.

The scores of UV-induced pigmented spots are negatively correlated with the consumption of total polyphenols (correlation coefficient R = -0.224), and the rate of development of hyperpigmented spots has been suppressed by the consumption of total polyphenols. Therefore, increased consumption of polyphenols may be beneficial in mitigating skin photoaging, and green tea contributes to suppressing skin hyperpigmentation by adding large amounts of polyphenols to the diet.

The precise mechanisms have not yet been elucidated, however, it has been proven that the consumption of green teas (Benifuuki tea and Yabukita tea) leads to a rise in the skin's free radical trapping activity by 28 and 29%, respectively. These free radicals, produced in response to oxidative stress from UV rays for example, are responsible for skin damage through the degradation of dermal fibers, which can cause an acceleration of skin aging. Green tea could therefore exert its effect on the signs of aging through its antioxidant capacity.

Finally, drinking green tea can generally result in healthier skin. In a study conducted by Wilhelm STAHL, the aim was to observe the effects of green tea polyphenols on the skin properties of 60 women. Over a period of 12 weeks, the participants consumed either a beverage containing green tea polyphenols providing 1402 mg of total catechins (a flavonoid in green tea) per day, or a control beverage. Photoprotection, skin structure, and skin function were measured at the start (week 0), at week 6, and at week 12.

After exposing skin areas to UV rays, the UV-induced erythema significantly decreased in the intervention group, by 16 and 25% after 6 and 12 weeks, respectively. The structural characteristics of the skin that were positively affected include elasticity, roughness, scaling, density, and water homeostasis. Consuming a green tea polyphenol-based beverage for 12 weeks increased blood flow by 29% and oxygen supply to the skin. Similarly, in a separate single-dose study (0.5, 1, and 2 g) of green tea polyphenols, blood flow was maximized 30 minutes after ingestion. In summary, it has been demonstrated that the green tea polyphenols contained in a beverage contribute to improving skin quality in women.

Maintaining skin integrity is vital for skin function and appearance, and requires an optimal intake of nutrients. It has been observed that the ingestion of green tea catechins improves skin hydration, transepidermal water loss (TEWL), density, and elasticity. The improvement in skin structure may also be linked to the increase in skin blood flow due to flavonoids. Microcirculation is important for the supply of nutrients and oxygen to the skin. In the previous study, skin blood flow increased in volunteers who consumed a green tea flavonoid-enriched beverage for 12 weeks. This finding could be one of the mechanisms involved in improving skin condition.

• MUKHTAR H. & al. Protection against ultraviolet B radiation-induced effects in the skin of Skh-1 hairless mice by a polyphenolic fraction isolated from green tea. Photochemistry and Photobiology (1993).

• STAHL W. & al. Green tea polyphenols provide photoprotection, increase microcirculation, and modulate skin properties of women. Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions (2010).

• GABRANI R. & al. Green tea extract: Possible mechanism and antibacterial activity on skin pathogens. Food chemistry (2012).

• LADEMANN J. & al. A randomized controlled trial of green tea beverages on the in vivo radical scavenging activity in human skin. Skin Pharmacology and Physiology (2017).

• KONDO K. & al. Consumption of polyphenols in coffee and green tea alleviates skin photoaging in healthy japanese women. Clinical, Cosmetic and Investigational Dermatology (2020).