A Recent Update on the Potential Use of Catechins in Cosmeceuticals

Abstract

Catechins are a type of flavonoid known for their beneficial functions as antioxidants and antibacterials. Recent research indicates the antioxidant potential of catechins on the skin. Catechin and epigallocatechin are reported to have significant potential in preventing ageing. Epigallocatechin gallate, gallocatechin gallate, and epigallocatechin can inhibit hyperpigmentation processes. Additionally, catechins exhibit potential in UV protection and inflammation inhibition in acne. Consequently, catechins are now being used in the cosmetics industry, with formulations containing catechins as the active ingredient developed to produce various products such as soap, sunscreen, creams, etc. Herein, this paper reviews the antioxidant potential of catechins for use in cosmetic formulations and the current status of clinical trials of catechins in cosmetics.

1. Introduction

Cosmetics are widely used by everyone and can be classified as decorative or skincare cosmetics. They are defined by BPOM Indonesia as materials or preparations intended for use on the external parts of the human body such as the epidermis, hair, nails, lips, and external genital organs, or on the teeth and oral mucous membranes, especially for cleaning, perfuming, changing the appearance and/or improving body odour, or to protect or maintain the body in good condition. Based on the literature, cosmetics are often used for aesthetic and self-care benefits, and that they also intersect with skin health. The skin is the largest human organ and protects the body from external insults, therefore, it is essential to care for the skin according to the unique needs of the individual. The term ‘cosmeceutical’ refers to a cosmetic product that provides medical effects and contains certain active compounds. These cosmeceutical products are not only for whitening, antiageing, and sunscreen purposes, but also for hyperpigmentation, photoageing, wrinkles, and hair loss [1]. It is important to note that cosmeceutical preparations are not intended to be given systematically, rather, they are applied locally/topically, that is, the ‘dermal delivery’ as the site of action is usually the stratum corneum (SC), the viable epidermis and/or dermis [2].

Skin ageing typically starts to manifest when an individual reaches their late 20s to early 30s due to two distinct sources [3]: intrinsic ageing, which results from issues within the network of elastin fibres and collagen, or extrinsic ageing due to exposure to environmental factors such as sun radiation. Oxidative stress triggers inflammation, constraining epidermal cell renewal and ultimately leads to a reduction in epidermal thickness and a weakening of the protective barrier [4]. Sun radiation triggers the creation of reactive oxygen radicals (ROS) that cause keratinocytes to generate pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α) and interleukin-8 (IL-8), thereby producing more ROS [5]. Excessive ROS leads to the development of wrinkles by causing the breakdown and abnormal interlinking of structural proteins such as glycosaminoglycans, collagen, and elastin fibres in the skin’s extracellular matrix. Hence, antioxidants isolated from natural products can be used to suppress ROS production to slow down skin ageing [6].

Catechins are natural flavan-3-ols (or flavonols), a type of polyphenolic compound belonging to the flavonoid family. They are present in a variety of fruits, vegetables, and plant-based beverages [7] and are particularly concentrated in tea leaves, red wine, broad beans, rock-rose leaves, apricots, black grapes, and strawberries. Epicatechin is abundant in chocolate, apples, broad beans, pears, black grapes, cherries, and certain types of berries including blackberries and rasp6berries [8].

Catechins offer numerous health benefits by effectively eliminating free radicals and slowing down the breakdown of the extracellular matrix caused by exposure to ultraviolet (UV) radiation and pollution. They stimulate collagen production while preventing the generation of matrix metalloproteinase enzymes. Due to the presence of hydroxyl in the gallate group, epigallocatechin gallate (EGCG) and epigallocatechin (ECG) can neutralise free radicals, surpassing several antioxidants like trolox, ascorbic acid, and tocopherol [9]. Thus, catechins have the potential to be used in cosmetic and dermatological products [10] and are now commonly included in pharmaceutical, medical, and cosmetic products. For example, a transethosomal gel form of catechins can reduce total cholesterol in mice [11] and Uncaria gambir is used to treat diarrhoea, sore throat, spongy gums, dysentery, arteriosclerosis, and obesity [12].

The anti-inflammatory and antioxidant properties of EGCG have been extensively examined for their impact on apoptosis, proliferation, and differentiation. EGCG is also used as a skincare ingredient due to its potential for skin hydration and as an anti-pigmentation agent, although further study is needed [13,14].

2. Physicochemical Properties of Catechins

Catechins are bioactive polyphenols and are typically isolated from green tea (Camellia sinensis L.) and gambir leaves (Uncaria gambir Roxb). There are a few types of catechins which possess the flavan-3-ol structure consisting of two benzene rings, a heterocycle dihydropyran, and a hydroxyl [15,16]. The structures are shown in Figure 1.

Catechins have been utilised in many pharmacological formulations [17,18]. The use of catechins is based on its physicochemical characteristics such as polarisability, dipole moment, molecular weight, surface area, and van der Waals volume, as well as macroscopic traits including solubility, octanol/water partition coefficient, acidity or basicity in solution, etc. [19]. In the Indonesian standard guide, namely the Indonesian Herbal Pharmacopoeia, there are several physicochemical profiles of catechins obtained from gambir plants (Uncaria gambir (Hunter) Roxb.) as shown in

Table 1. Physicochemical parameters of catechins based on the Pharmacopeia handbook.

Physicochemical Parameters	Accepted Value	Reference
Organoleptic	Solid form, it appears as a light brown to dark reddish-brown substance with a distinctive odour. It possesses a chelate taste that is slightly bitter at first but ends with a sweet aftertaste.	[20]
Water Content	Quantity should not exceed 14%	[20]
Ash Content	Quantity should not exceed 0.5%	[20]
Ash, not soluble in acid	Quantity should not exceed 0.1%	[20]
Purity	Contains no less than 90% tannins counted as catechins.	[20]
Identification	The assay was carried out using spectrophotometry with a wavelength of 294 nm.	[20]
Molecular weight	290.27 g/mol	[20]
Solubility	Soluble in water and polar organic solvents; soluble in pressurised hot water between 298.75 to 415.85 K; soluble in mixtures of supercritical carbon dioxide (SC-CO2) and ethanol at 313 K and pressures ranging from 80 to 120 bar; soluble in SC-CO2 between 313.15 and 343.15 K and pressures ranging from 12 to 26 MPa using ethanol as the co-solvent.	[21]

.

3. Activities of Catechin

3.1. Antioxidant

Antioxidants scavenge oxygen free radicals (singlet and triplet), ROS, peroxide decomposers, and enzyme inhibitors to protect vital molecules from harm [22]. The use of antioxidants derived from natural ingredients is increasing. Natural antioxidants can be single pure compounds/isolates, combinations of compounds, or plant extracts. The secondary metabolites, polyphenols, are the most common phyto-antioxidants [23]. Polyphenols have benzene rings with attached -OH groups which determine the antioxidant activity based on their number and position [24]. Protein phosphorylation is influenced by phenol groups by inhibiting lipid peroxidation. Flavonoids are the main source of polyphenols, while carotenoids are the most abundant sources of terpenes [25].

Catechin produces and discards free radicals [26] through several key direct and indirect antioxidant mechanisms. The direct mechanism involves the scavenging of ROS, whereas the indirect mechanism occurs through increased antioxidant enzymes and the inhibition of the pro-enzyme that participates in oxidant stress [8,27]. The phenolic hydroxyl group in catechin is involved in the scavenging of ROS, therefore more hydroxyl groups will improve the antioxidant activity. According to the structure, the hierarchy of antioxidant activity of catechins is EGCG, EGG, EGC, EC, and, lastly, catechin [8].

The structural characteristics of flavan-3-ols, specifically their resorcinol and catechol components, which consist of A and B rings connected by the Pyron ring (C ring), are responsible for their antioxidant properties (Figure 1) [28]. The ability of flavan-3-ols to scavenge radicals primarily relies on the arrangement of hydroxyl groups and their capacity to donate hydrogen atoms [29]. The stability of the phenoxy radical produced after hydrogen atom transfer (HAT) also plays a role in their ability to counteract reactive oxygen radicals [30]. Catechins can exist in four different diastereoisomers, which arise from two chiral centers (2ⁿ) at C2 and C3. These diastereoisomers are referred to as (+) catechin (2R, 3S), (−) epicatechin (2R, 3R), (−) catechin (2S, 3R), and (+) epicatechin (2S, 3S) [31]. Overall, the stereoisomerisms are determined by the positioning of the B ring connected to the C ring at the C2 atom and also the chirality of R1 and R2 attached to the C ring at the C3.

The structures are indicative of a site of a projected bond—R stands for dashed wedge bonds that extend away from the viewer, and S represents solid wedge bonds that project out of the paper towards the viewer, as seen in Figure 2. The degree of polymerization also plays a role in determining the antioxidant properties [32]. The capability of catechin and epicatechin to scavenge radicals is attributed to the dihydroxyl group at C-3’ and C-4’ on the B ring, a C3-hydroxyl group on the C ring without a 2,3 double bond, and hydroxyl groups at C5 and C7 on ring A. In this context, the catechol ring (B) exhibits greater electron-donating capacity than the other rings because it contains an ortho-dihydroxyl group (detail see Figure 2 and Figure 3) [33]. The scavenging of free radicals by the hydroxyl groups occurs via hydrogen atom transfer and single-electron atom transfer, with catechin undergoing oxidation to form the relatively reactive quinone [34] as could be observed from Figure 4.

Numerous studies have reported that the primary source of antioxidant activity in CT and ECT is their elevated redox characteristics. The antioxidant properties of catechin and epicatechin, which are found in different plant extracts, were assessed using various experimental antioxidant tests, including ferric reducing antioxidant power (FRAP), 1,1-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO), and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS⁺), demonstrating that CT and ECT exhibit strong antioxidant capabilities [35]. CT and ECT share a similar molecular structure, but they exhibit distinct chemical reactivity properties because CT’s antioxidant capability relies on its planar geometry, whereas ECT’s antioxidant activity is due to the interaction of hydrogen bonds at the catechol moiety. The lack of a double bond at C2 = C3 in the C ring significantly affects ECT’s antioxidant capacity. Additionally, it has been demonstrated that the reactivity of flavan-3-ols is thermodynamically modified depending on the solvents used [36].

There are many uses of catechins. Aside from being used as pure antioxidant compounds, catechins can be formulated into many products including sunscreen, lip balm, anti-dandruff shampoo, cosmetic cleansers, and cosmetic creams. They have also been extracted from many natural sources, as detailed in

Table 2. Antioxidant activity of catechins from various sources.

Methods	Sample	Result	Ref.
DPPH Assay	Camellia sinensis	Solvent Used: Methanol Green Tea = 67.3% White Tea = 47.9% Black Tea = 28.9%	[37]
	Lepisanthes alata (Blume) Leenh	Solvent Used: Water Rind: 61.61% Flesh: 47.93% Seeds: 48.66% Whole Fruit: 69.30% Leaves: 59.35% Bark: 49.91%	[38]
		Solvent Used: Methanol Rind: 86.17% Flesh: 27.47% Seeds: 89.58% Whole Fruit: 78.34% Leaves: 61.71% Bark: 87.03%
		Solvent Used: Ethanol Rind: 85.81% Flesh: 21.23% Seeds: 90.12% Whole Fruit: 46.20% Leaves: 79.61% Bark: 87.03%
	Sterculia quadrifida R.	Bark: 51.5 µg/mL (50%)	[22]
Malondialdehyde	Uncaria Gambir Roxb	Dose of 5 mg/kg: 0.19% Dose of 10 mg/kg: 31.28% Dose of 20 mg/kg: 57.63% Control + (Vit E): 5.55% Control-: −77.79%	[39]
	Uncaria Gambir Roxb.	Varies from 2.732% to 3.792%	[40]
	Combination of Isolated Catechin and Quercetin	Insignificant antioxidant activity Dose of catechin used was 100 µg/mL (p < 0.05)	[41]

.

In the context of the skin, several studies indicate that antioxidants play a crucial role in inhibiting the effects of radiation [42]. The various roles of antioxidants on the skin are presented in

Table 3. The various roles of antioxidants on skin.

Antioxidant Function	Mechanism of Action	Reference
Anti-ageing	Antioxidants inhibit the action of superoxide dismutase (SOD) enzymes, which play a role in degrading collagen.	[43]
Skin Brightening	Antioxidants have whitening effects by inhibiting tyrosinase and act as anti-inflammatory agents for hyperpigmentation caused by UV exposure (commonly known as melasma).	[44]
UV Filters	Topically administered antioxidants can enhance the photoprotective capabilities of UV filters by reducing erythema, inhibiting the development of sunburned skin cells, and causing immunosuppression.	[45]
Skin Hydration and Anti-Hyperpigmentation	Antioxidants suppress the production and secretion of melanin in melanoma cells to enhance skin hydration and improve hyperpigmentation.	[46]

.

3.2. Anti-Ageing

Elastase, a protein kinase enzyme, cleaves specific polypeptide bonds to reduce elastin levels. Preventing elastase functions within the dermis layer can be utilised to maintain the skin’s flexibility, therefore, elastase activity inhibitors can serve as cosmetic ingredients to counteract the signs of skin ageing [47]. Polyphenols found in isolated white tea inhibit collagenase and elastase enzymes, specifically catechin and EGCG (Figure 5). Furthermore, given that collagenase is a zinc-containing metalloproteinase, these catechins could potentially attach to the Zn²⁺ ion present in the enzyme, thereby obstructing its ability to bind to the substrate [48].

3.3. Skin Brightener

Catechin directly inhibits tyrosinase activity and reduces the expression of tyrosinase [49]. EGCG, GCG, and EGC demonstrate great potential as tyrosinase activity inhibitors [50]. The catechins have a substantial inhibitory effect on tyrosinase activity and melanin production by downregulating the cAMP/CREB/MITF signalling pathway in B16F10 cells (Figure 6), with ECG demonstrating the strongest effect, followed by EGCG and GCG [51]. EGCG also suppresses the production of melanin induced by α-MSH in B16 melanoma cells [49].

3.4. Anti-Hyperpigmentation

UV radiation results in melanogenesis. The mass production of melanin in the skin minimises UV radiation but causes the skin to slightly darken to a brownish color. Catechin as a depigmentation agent will inhibit melanin formation by inhibiting melanin synthesis through tyrosinase (TYR) and microphthalmia-associated transcription factor (MITF). MITF is a transcription factor that is responsible for melanocyte development in melanogenesis. Catechin will inhibit MILTF, thereby preventing melanocytes from producing melanin and hyperpigmentation [52].

3.5. UV-Reduction and Sunscreen

UV radiation is categorised into UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (280–100 nm). Continuous exposure to UV-B radiation can lead to disruptions in the skin caused by free radicals and ROS, which stimulate melanin production and melanocyte proliferation. Tyrosinase facilitates melanin synthesis and represents a pivotal point in melanogenesis. High melanin levels can disrupt pigmentation in human skin, leading to conditions such as age spots, melasma, malignant melanomas, and freckles. EGCG is acknowledged as a natural antioxidant to neutralise free radicals, modulate the activity of antioxidant enzymes, diminish the effects of oxidative stress, and inhibit tyrosinase activity [53].

Sunscreen is a cosmetic that functions as a skin protector [54], filtering UV to reduce the radiation emitted from the sun [55,56]. Aromatic compounds conjugated to carbonyl groups convert UV energy into minimised UV energy [51], preventing the chemical properties of UV-absorbing potency without the need for significant photodegradation (Figure 7). The usage of sunscreen is determined based on the Sun Protection Factor (SPF), which is defined as the ability to supply a minimal erythema dose (MED) on the skin divided by the variable of UV energy that is needed to supply MED on unprotected skin [57].

The higher the SPF, the more protective the sunscreen [58] to prevent sunburn as well as skin cancer in the long term. The SPF can be determined with in vivo or in vitro methods. The in vivo test involves human volunteers while the in vitro is differentiated through two categories: measuring the UV absorption or transmission of the test product or spectrophotometric analysis. Effective sunscreen products at least need to have an absorbance of 290 to 400 mm [59].

3.6. Anti-Acne

Acne is a skin disease caused by the overgrowth of Staphylococcus epidermidis and Propionibacterium acnes. Some recent research showed that catechin from gambir and green tea could inhibit the growth of acne pathogens. Recent research showed the MIC of catechin as anti-acne is 0.1%. Another study showed that the inhibition zone of catechin is 18.45 mm for P. acnes and 15.68 mm for S. epidermidis [60]. The antibacterial mechanism of catechin involves disrupting the cell membrane and inhibiting intracellular enzymes (Figure 8). The mechanism of catechin to counter acne inflammation is through the inhibition of the pro-inflammatory cytokines IL-8 and TNF-α [61].

4. Application and Development of Catechin Formulations in Cosmetic Preparations

The skin serves as the protective outer covering and comprises three primary structural layers: The outermost part is the epidermis, the middle layer is the dermis, and the innermost part is the subcutaneous layer [62]. Over time, the skin experiences alterations influenced by various external and internal factors. These skin changes represent some of the most apparent ageing indicators and encompass features such as loose skin, fine lines, dryness, and age-related spots, often accompanied by a reduction in fat content and natural skin smoothness [63]. Since catechin is a potential antioxidant agent [34], numerous cosmetic and skincare products have been developed using catechin extracts as their main ingredient including soaps, sunscreens, shampoos, and lip balms (

Table 4. The formulation of catechin as cosmetics modified from various formulations.

Dosage Form	Formulation	Evaluation Available	Reference
Solid Soap	Catechin (obtained from extract), Aquadest, EDTA, Olive oil, Palm oil, Stearic acid	Organoleptic: solid, brown, smelly Foam Test: varies from 50.94% to 64.78% pH Test: around 8–9 Moisture content: 15%	[64]
Sunscreen	Catechin, Cera alba, Tween 80, Ceryl Alcohol, Stearyl Alcohol	Organoleptic: stable in colour pH: 4.2–7.4 SPF: 16	[65]
	Gambir Leaf Extract, Glycerin, Triethanolamine, Propylene Glycol, Aquadest	Organoleptic: physically stable during storage pH: 5.55–6.93 SPF: 7 to 26.55	[66]
Solid Shampoo	Sodium Cocoyl Isethionate, Coco Glucoside, Beeswax, Shea Butter, Panthenol, Essential Oil, Lactic Acid, Tocopherol, BHT, Mango Peel Extract (containing catechin)	Organoleptic: physically stable with surface tension of water to at least 40 mN/m pH: 6.0–7.0 Accelerated thermal stability test: no change regarding the texture, smell, and colour Oxidative stability: low oxidation state	[67]
Lip Balm	Catechin Extract, Ethyl Alcohol, Lanolin, Cera alba, Propylene Glycol, Oleum rosae, Nipagin, Dye, Liquid Paraffin	Organoleptic: physically stable during storage Irritation Test: does not show irritation	[65]
Cream	Gambir Leaf Extract, Stearic Acid, Cetyl Alcohol, Paraffin, Isopropyl Myristic, Methylparaben, Triethanolamine, Glycerine, Perfume, Aquadest	Organoleptic: yellow or green cream that is homogeneous and non-greasy pH: 7.24–7.80	[68]
Pell-Off Gel Mask	Catechins, PVA, PVP K-30, Propylene Glycol, Methylparaben, Propylparaben, Ethanol 70%, Citrus Essential Oil, Distilled Water	Organoleptic: pale yellow to light brown and featuring a scent reminiscent of oranges pH: 5.39–5.92 Irritation Test: does not show irritation	[69]

).

Zeng, 2017, found that tea polyphenols at pH 3–6 remained stable during storage at 4 and 25 °C. The more the pH decreases, the more stable the solution is. The color of the tea polyphenol solution changed from green to dark yellow with increasing temperature. The total catechin content decreased significantly when heating reached 100 °C, in addition to epimerization [70].

The pH influences the stability of catechins, with catechins being more stable at a low pH, providing more stable antioxidant activity. Temperature and light also affect stability, thus it is necessary to make appropriate formulations to maintain their stability in preparations [15]. Active compounds for topical antioxidant purposes must penetrate through the stratum corneum and enter the deeper layers of the skin but should not enter the blood vessels so that they circulate in the body. It reported that on catechin permeation, catechins are retained in the stratum corneum [15].

In another research study, Yamamoto et al. developed a novel methylated catechin produced (Figure 9) by using, as a substrate, epigallocatechin-3-O-gallate, epicatechin-3-O-gallate, or an isomer thereof. These researchers found that the novel methylated catechins can be efficiently manufactured using catechins such as EGCG as substrates. Furthermore, the novel methylated catechins obtained have excellent effects such as antiallergic, anticancer, anti-obesity, anti-arteriosclerosis, antihypertensive, and antimicrobial effects and can be applied to various products such as food and beverage products, pharmaceutical drugs, quasi-drugs, and cosmetics [71]:

The liposomal form is considered to be the best protection against possible oxidation of polyphenolic compounds. This structure is able to encapsulate both hydrophilic and lipophilic compounds, protecting them from degradation and dilution in systemic circulation. The interaction between phosphatidylcholine as a component of liposomes and polyphenolic compounds is due to the formation of hydrophobic and covalent bonds between them. This phenomenon causes a decrease in lipid absorption, while the lipids trap and protect the polyphenols. Phenolic compounds such as anthocyanins, ferulic acid, resveratrol, quercetin, and EGCG are already available in the cosmetic market in liposomal form. The liposomes have a particle size range of 50–500 nm. This form not only protects against polyphenol degradation but also enhances skin absorption [72].

5. Pre-Clinical Dan Clinical Trials of Catechins in Cosmetics and Skincare

Table 5 details the clinical trials of catechin-containing cosmetics. As of November 2023, there is an ongoing trial to determine the effect and safety of tea catechins performed by the H. Lee Moffitt Cancer Center & Research Institute. The latest trials of catechin were performed by Farrar in 2015 with the team of the Centre for Dermatology and Institute of Inflammation and Repair in Manchester, showing little to no effect of catechin from green tea on sunburn. Even with the currently available information, it is worth mentioning that catechin has an abundance of pharmacological activities that could be used as potential treatments for many diseases. The trial of catechin as an antioxidant as part of cosmetic function would increase the understanding of catechin as a multifunctional compound. Although the 2015 trial shows little potential for catechin to reduce UV, a modification and revision of the method in the future is worthy of investigation [73].

In a study on skin whitening in vivo, the catechin’s transfersome form was found to have better permeation compared to the solution form of the catechin. It was also effective in inhibiting thyrokinase and was well-tolerated in guinea pig test animals. These results suggest that catechin-containing transferosomes could be a potential treatment strategy for UV-induced oxidative damage to the skin through topical administration [74].

Table 5. Clinicals trials of catechins.

Study Title	Catechin	Result/Conclusion	Ref.
Double-blinded, placebo-controlled trial of green tea extracts in the clinical and histologic appearance of photoageing skin	Green Tea, EGCG	Skin elasticity No significant differences, although histologic grading showed improvement in elastic tissue Experiment: supplement of green tea and addition of 10% green tea cream in an 8-week trial	[75]
The green tea polyphenol (-) epigallocatechin gallate and green tea can protect human cellular DNA from UV and visible radiation-induced damage	Green Tea, EGCG	Photoprotective UV radiation inhibition, prevention, and minimal DNA cell damage Experiment: study of 540 mL of green tea in 10 subjects	[76]
A randomised controlled trial of green tea beverages on the in vivo radical scavenging activity in human skin	Green Tea, EGCG	Antioxidant Increasing radical scavenging of skin by 28–29% compared to the control group Experiment: 3 cups of tea (Benifuuki tea and Yabukita tea) for 3 weeks	[77]
UV radiation-induced degradation of the dermal extracellular matrix and protection by green tea catechins	Green Tea, EGCG	Photoprotective Specific UVR protection and significant changes in acute UVR Experiment: 50 subjects were randomised to green tea catechin and vitamin C for 12 weeks with twice-daily consumption	[78]
Treatment of atopic dermatitis associated with Malassezia sympodialis by green tea extracts bath therapy: a pilot study	Green Tea, EGCG	Atopic dermatitis Significant improvement in 1 of 3 patients with a total reduction of 50.3% Experiment: 3 subjects bathed in a combination of green tea extract and tap water for 1 month	[79]
A randomised controlled trial of green tea catechins in protection against UV radiation-induced cutaneous inflammation	Green Tea, EGCG	Photoprotective No significant difference between the test and placebo groups Experiment: 50 subjects were randomly placed in 2 groups; group 1 was given encapsulated green tea extract with the addition of vitamins and group 2 was given a placebo twice daily for 3 months	[73]
Formulation of Gambir (Uncaria gambir Roxb.) ethanol extract as acne powder	Gambir Extract, Catechin	Anti-acne Inhibition diameters of 3%, 6%, and 9% produced a diameter of 3.6 mm, 4.2 mm, and 6.8 mm respectively Experiment: catechin from an ethanol extract of gambir (3%, 6%, and 9%) tested on Staphylococcus epidermidis	[60]
The use of green tea extract in cosmetic formulation: not only antioxidant active ingredient	Green Tea Leaf Extract	Moisturiser Significant increase in skin moisture and improved skin texture Experiment: cosmetic formulation with 6% Camellia sinensis extract with 24 volunteers	[80]

Table 5. Clinicals trials of catechins.

Study Title	Catechin	Result/Conclusion	Ref.
Double-blinded, placebo-controlled trial of green tea extracts in the clinical and histologic appearance of photoageing skin	Green Tea, EGCG	Skin elasticity No significant differences, although histologic grading showed improvement in elastic tissue Experiment: supplement of green tea and addition of 10% green tea cream in an 8-week trial	[75]
The green tea polyphenol (-) epigallocatechin gallate and green tea can protect human cellular DNA from UV and visible radiation-induced damage	Green Tea, EGCG	Photoprotective UV radiation inhibition, prevention, and minimal DNA cell damage Experiment: study of 540 mL of green tea in 10 subjects	[76]
A randomised controlled trial of green tea beverages on the in vivo radical scavenging activity in human skin	Green Tea, EGCG	Antioxidant Increasing radical scavenging of skin by 28–29% compared to the control group Experiment: 3 cups of tea (Benifuuki tea and Yabukita tea) for 3 weeks	[77]
UV radiation-induced degradation of the dermal extracellular matrix and protection by green tea catechins	Green Tea, EGCG	Photoprotective Specific UVR protection and significant changes in acute UVR Experiment: 50 subjects were randomised to green tea catechin and vitamin C for 12 weeks with twice-daily consumption	[78]
Treatment of atopic dermatitis associated with Malassezia sympodialis by green tea extracts bath therapy: a pilot study	Green Tea, EGCG	Atopic dermatitis Significant improvement in 1 of 3 patients with a total reduction of 50.3% Experiment: 3 subjects bathed in a combination of green tea extract and tap water for 1 month	[79]
A randomised controlled trial of green tea catechins in protection against UV radiation-induced cutaneous inflammation	Green Tea, EGCG	Photoprotective No significant difference between the test and placebo groups Experiment: 50 subjects were randomly placed in 2 groups; group 1 was given encapsulated green tea extract with the addition of vitamins and group 2 was given a placebo twice daily for 3 months	[73]
Formulation of Gambir (Uncaria gambir Roxb.) ethanol extract as acne powder	Gambir Extract, Catechin	Anti-acne Inhibition diameters of 3%, 6%, and 9% produced a diameter of 3.6 mm, 4.2 mm, and 6.8 mm respectively Experiment: catechin from an ethanol extract of gambir (3%, 6%, and 9%) tested on Staphylococcus epidermidis	[60]
The use of green tea extract in cosmetic formulation: not only antioxidant active ingredient	Green Tea Leaf Extract	Moisturiser Significant increase in skin moisture and improved skin texture Experiment: cosmetic formulation with 6% Camellia sinensis extract with 24 volunteers	[80]

6. Conclusions

Catechins are flavonoids found in various plants and particularly abundant in certain foods and beverages, particularly in green tea, as well as in some fruits, such as apples and berries. These compounds have gained attention in the field of cosmeceuticals due to their potential skincare benefits. Cosmeceuticals are cosmetic products that contain biologically active ingredients with potential pharmaceutical properties designed to improve skin health and appearance. Catechins are commonly incorporated into various cosmeceutical products such as creams, serums, toners, and masks, and are often paired with other skincare ingredients for enhanced benefits. When considering products containing catechins, it is essential to consider factors like product formulation, concentration, and the specific type of catechin used. As with any skincare product, it is a good idea to consult with a dermatologist or skincare professional to determine which catechin-containing products are most suitable for specific skin concerns and needs. Additionally, it is important to perform a patch test before using any new cosmeceutical product to ensure that it does not cause adverse reactions.