Green tea extract may become your skin 'guardian'

The main component of green tea polyphenols is EGCG (that is, epigallocatechin gallate). EGCG has been proven to have multiple health benefits. Its properties range from antioxidants to anti-inflammatory, and it is beneficial to cardiovascular health, cancer prevention, reducing the risk of cognitive dysfunction, improving diabetes, and helping to lose weight.

1. EGCG can prevent skin cancer and reduce UV damage
EGCG has anti-ultraviolet properties and may play a preventive role in the development of skin cancer. According to reports, EGCG treatment can reduce collagen synthesis and fibroblast collagenase secretion in mice (24-hour post-treatment). Because the typical representative of UV-induced intracellular damage is to affect collagen synthesis and collagenase secretion levels.

In addition, by measuring UVB-induced guinea pig erythema, UVB-induced damage was quantified. EGCG has been reported to significantly reduce erythema within 24 hours after irradiation.

Another study also analyzed the effect of EGCG on epidermal Langerhans cells (LCs) and described the decrease in cell number under UV irradiation. Histological tests showed that the EGCG-treated participants had a 58% reduction in skin LCs damage compared to the control group. The dose-dependent effects of green tea polyphenols were tested with different concentrations (1-10%). When the concentration is 2.5% or higher, it shows proper protection.

These results are consistent with a recent study that detected UV-induced DNA oxidative damage by measuring CD1a+ cell depletion and UV-induced anti-8-hydroxy-2-deoxyguanosine (8-OHdG) production. 8-OHdG is associated with UV-induced nucleic acid modification.

Compared with non-irradiated skin, green tea treated skin exposed to ultraviolet light had a 35% reduction in CD1a+ cells. After irradiation, the treated skin of the vehicle decreased by 57%, similar to the untreated skin.

The level of 8-OHdG in the skin that was applied with green tea extract and exposed was not significantly different from that of unirradiated skin. However, the vehicle-treated skin showed higher levels of 8-OHdG.

In addition, EGCG has been reported to reduce UV-induced dermal and epidermal production of H2O2 and NO, and inhibit the infiltration of CD11b+ cells (CD11b+ is a marker on the surface of macrophages and neutrophils), which is an indicator of oxidative stress. EGCG can also inhibit the production of epidermal lipid peroxidation (LPO) and have a positive effect on the levels of other Antioxidants (GSH).

A similar study, involving mice of the same type, provided additional information about the extent to which EGCG induces apoptosis in tumor and non-tumor areas irradiated by UVB. After 20 weeks of UV-B irradiation, the mice received EGCG treatment once a day, 5 days a week for 18 weeks. This treatment resulted in 72% increase in apoptosis of non-malignant tumor cells and 56% increase in apoptosis of squamous cell carcinoma cells, but no effect on proliferative or non-tumor areas.

2. Synergy of EGCG and other ingredients in cosmetics
Based on the future development of EGCG-based skin products, the study of the interaction between the most common cosmetic ingredients and EGCG is established.

1) Vitamins
In addition to being used to treat acne, Vitamin A has anti-photoaging and anti-wrinkle properties and can be used in cosmetics. A derivative of vitamin A, all-trans retinoic acid (ATRA), has been shown to help EGCG inhibit the growth of mouse B16 melanoma cells (a special type of melanoma known for its high metastatic rate).

In addition to the common properties of vitamin C and A (anti-wrinkle and anti-aging), vitamin C has been shown to enhance skin whitening. In addition, vitamin C reduces the photo-induced photochemical degradation of EGCG and also improves the preservation of its antioxidant properties. Studies have shown that vitamin C can increase the stability of EGCG molecules, especially in the water environment.

On the other hand, although the concentration of EGCG is significantly lower than vitamins, it is reported that EGCG can enhance the lipid antioxidant effects of vitamin C and vitamin E.

Vitamin E is also an antioxidant and a very important cosmetic ingredient. As mentioned earlier, it does not enhance the stability of EGCG. One form of alpha-tocopherol (vitamin E) has been shown to actively interact with EGCG. EGCG protects hydroperoxylinoleic acid (LoaOOH) caused by endothelial cell damage, and α-tocopherol strengthens the protection of EGCG.

2) Titanium Dioxide (TiO2), UV filter
Titanium dioxide (TiO2) is a very common ingredient in many cosmetics. If it is used in sunscreen, it will appear at a nano-level concentration because it absorbs ultraviolet light and forms a transparent sunscreen film when used topically. In addition, if it is used in its main form (pigment grade) to brighten food, toothpaste and some medicines.

A 2016 study analyzed the interaction between EGCG and TiO2. Nano titanium dioxide is coated with green tea extract (GTE), of which EGCG content is the most abundant. GTE coating reduces the photocatalytic activity of TiO2. Therefore, the coated version of TiO2 seems to be more suitable for sunscreen cosmetic applications.

3) Hyaluronic acid
Hyaluronic acid (HA) has strong moisturizing properties and is a very common cosmetic ingredient. A 2017 in vitro study examined the interaction between HA and EGCG. The transporter of EGCG and HA on the skin of male Wistar rats after excision has better antioxidant effect, and has higher skin permeability and deposition.

4) Isopropyl myristate
Isopropyl myristate increases skin penetration. Compared with the other four polyphenols, EGCG has the second highest drug loading and the second slowest release time. These two characteristics are very important for the development of external emulsions.