Enhancing Sun Protection: Formulating and Assessing Herbal Sunscreen Formulations

Introduction

The skin serves various essential roles, including protecting the body against different forms of harm, pathogens, thermal and chemical damage, and exposure to ultraviolet (UV) radiation.¹ Superficial factors pose a risk for the skin, with UV radiation being the most harmful.

UV radiation is abundant in the environment and can cause various skin problems, such as inflammation, premature aging, and cancer.² UV radiation can penetrate the skin and interact with cells located within the skin, specifically with fibroblasts and keratinocytes.³ UV radiation is composed of three components: UVA (with a wavelength of 320-400 nm), UVB (with a wavelength  of 280-320 nm), and UVC (with a wavelength of 100 280 nm). It should be noted that UVC radiation poses a particular risk to the skin.⁴ The effect of UV rays on the skin is shown in Figure 1.

Photoprotective agents such as sunscreens help safeguard the skin by preventing and reducing damage caused by the harmful effects of UV rays.⁵

Sunscreen effectiveness is typically measured by its sun protection factor (SPF), which is determined by the amount of UV energy required to cause minimal erythema (a noticeable reddening of the skin) in protected skin, divided by the amount of UV energy required to cause the same level of erythema in unprotected skin.⁶

Herbal sunscreen, also known as herbal sunblock or herbal suntan lotion, is a topical product that shields the skin from the sun’s harmful UV radiation. Its primary aim is to mitigate the risk of skin cancer. The use of herbal sunscreens has several benefits, including:

• Easy accessibility.

• Absence of side effects.

• No specialized equipment is required for preparation.

• Use of renewable resources and the availability of botanical ingredients at a low cost.

• Selectively absorb light within the 280-320 mm range.

• Remain stable in the presence of heat, light, and perspiration.

• Non-toxic and irritation-free.

• Have slow absorption.

• Readily dissolve in a suitable medium and exhibit neutrality.⁶

Plants contain phenolic and flavonoid compounds, which possess antioxidant properties. These bioactive constituents can absorb UV radiation and counteract the free radicals generated in the skin because of exposure to UV radiation.⁷ Phytoconstituents are becoming increasingly popular as ingredients in sunscreen products due to their ability to safeguard the skin against both internal and external harmful agents.⁸ Natural chemicals found in fruits, vegetables, medicinal plants, algae, and lichens such as polyphenols, carotenoids, and vitamins, are more effective than synthetic chemicals. This is due to their long-term benefits against free radical-induced skin damage and UV radiation.⁹ Classification of sunscreen with FDA-approved ingredients is shown in Figure 2.

Mechanism of action of employed phytochemicals in skin protection from harmful UV rays

Beetroot

The skin-protective benefits of beetroot against harmful UV rays can be attributed to its high content of betalains, flavonoids, and carotenoids. Betalains work to eliminate free radicals generated by UV exposure, reducing oxidative stress and DNA damage. Flavonoids, on the other hand, promote skin health and reduce inflammation. At the same time, carotenoids such as α-carotene and β-carotene offer an added protection against UV-induced skin damage and premature aging.^{10, 11}

Flax seeds

Flax seeds contain lignans that possess antioxidant and anti-inflammatory properties to shield the skin from early aging and harmful skin cancer. Omega-3 fatty acid and alpha-linolenic acid (ALA) in flax seeds promote skin hydration and help reduce pesky wrinkles. Furthermore, the presence of vitamin E safeguards against UV rays and environmental aggressors, keeping the skin healthy and radiant. ^12–14

Green tea

Green tea phytochemicals (GTPs) are crucial in safeguarding the skin against the harmful effects of excessive sun exposure. They have been proven to protect the skin by utilizing anti-inflammatory, antioxidant, and DNA repair attributes. These properties make GTPs a powerful solution for protecting the skin.¹⁵ One of the fundamental properties of GTPs is their ability to reduce inflammation caused by sun exposure, a common factor in skin damage and cancer. With powerful antioxidant abilities, these phytochemicals combat the reactive oxygen species (ROS) produced by the sun, preventing oxidative stress and DNA damage. Green tea phytochemicals work at all skin cancer development stages, effectively intervening and protecting the skin. Furthermore, they aid in DNA repair, an essential process in minimizing the risk of skin cancer from UV rays. In short, incorporating green tea phytochemicals into the skincare routine is vital for achieving and maintaining healthy skin.¹⁶

Materials and Methods

Materials

Analytical-grade ethanol was purchased from (Aqlivia Pvt. Ltd.). Beetroot, flax seeds, and green tea were purchased from the local market of Bengaluru.

Method

In-vitro evaluation of SPF

Various studies, including those by Fourneron et al. (1999), Gordon (1993), Mansur et al. (1986), Pissavini et al. (2003), and Walters et al. (1997) have determined the absorption characteristics of sunscreen agents through spectrophotometric analysis of dilute solutions. Mansur et al. (1986) proposed a simple mathematical equation to replace the in-vitro method that Sayre et al. (1979) introduced using UV spectrophotometry.

SPF = CF x 290Σ320 EE (ʎ) x I(ʎ) x Abs (ʎ)

Were, EE(ʎ): erythemal effect spectrum

I: Solar intensity spectrum

CF: Correction factor (=10)

(ʎ): wavelength¹⁷

constants of EE × I are shown in Table 1.

Preparation of hydroalcoholic extracts

A 10 g sample (Beetroot, flax seed, and green tea extracts) is mixed with 60 ml distilled water and 40 ml methanol in a 150 ml beaker. The mixture is left to extract overnight and then filtered. The filtrate is centrifuged at 2000 rpm for 20 minutes, producing a clear solution. The solution is diluted with methanol and zed for absorbance using UV spectroscopy.¹⁸ Hydroalcoholic extracts are shown in Figure 3.

In-vitro SPF determination procedure for hydroalcoholic extract

1 ml of the hydroalcoholic extracts was transferred into a 10 ml volumetric flask, and methanol was added to reach the flask’s mark. The mixture was ultrasonicated for 10 minutes at 28°C. 1 ml sample from the top was discarded, and the remaining sample was collected after cotton filtration. The samples were then analyzed using a 1 cm quartz cell to obtain absorption spectra from 290 to 450 nm, with methanol as a blank. Absorption data were collected at 5 nm intervals from 290 to 320 nm, with three replicates at each point. The Mansur equation was applied to the data obtained.

In-vitro SPF determination procedure for formulated sunscreen

The absorption spectra of the sample were determined by diluting 1g of the sample with 50 ml ethanol in a 100 ml volumetric flask. The solution underwent ultrasonication for 10 minutes at 28°C, followed by filtration through cotton. 10 ml sample from the top was discarded, and the remaining solution was collected. Absorption spectra were measured in the 290 to 450 nm range using a 1 cm quartz cell, with ethanol as the reference solution. Absorption measurements were taken at 5 nm intervals within the 290 to 320 nm range, with three replicates at each wavelength. The data were processed using the Mansur equation.

Development of formulation

Four cream bases were created using safe skin components through an emulsification process. The cream bases consisted of an oil phase and an aqueous phase, which were heated separately and then combined while stirring, and the mixture solidified at room temperature.¹⁹ The composition of the initial four creams is depicted in Figure 4. 

Evaluation of formulation

Physical parameters

The arrangement of outcomes in a table and figure shown in the results determines appearance and color.

Subjective parameters

The feel and consistency of the sunscreen were determined.

Thermal stability

The cream’s resistance to oil separation was tested in a humidity chamber at 60%-70% relative humidity and 37±1°C. A 20 mm wide and 5 mm thick layer of cream was applied to the internal wall of a 100 ml chamber. The cream underwent an 8-hour test period, and a successful outcome was defined as no oil separation.²⁰

pH determination

The quality of a sunscreen is evaluated by measuring its pH value using a digital pH meter during different storage conditions. Multiple formulations are tested periodically to monitor pH changes, aiming for an ideal pH of around 6.0, similar to the skin’s pH. pH variations can indicate chemical reactions and offer insights into product quality.²¹

Spreadability

A clear glass slide was taken, and a small amount of sunscreen was placed on it. Another glass slide was placed on the sunscreen and pressed gently to make a sandwich. The top slide was removed, and the diameter of the sunscreen spread was measured using a ruler. The test was repeated three times, and the average diameter was calculated using the formula A=πr2, where r is the spread’s radius (half of the diameter). The spreadability index (SI) was calculated using the formula SI= A/m, where m is the mass of the sunscreen.

Results 

Hydroalcoholic extracts Beetroot underwent an extraction process where half of its initial 10 g mass was successfully isolated, leaving 5g behind. In the case of flax seeds, an extraction yield of 60% was achieved, resulting in a remaining mass of 4 g out of the initial 10 g. Likewise, an 80% extraction rate was attained when processing green tea, leaving only 2 g from the original 10 g mass.

In-vitro SPF determination of herbal extracts used in the sunscreen.

All initial parameters and spectroscopic analyses met the established standards in the previous literature. Therefore, the chosen phytochemicals were subjected to further processing to determine their SPF values (Table 2). The SPF of flax seed, beetroot, and green tea were found to be 2.84, 11.33, and 2.26, respectively. The sum of SPF of all three ingredients was 16.43, which was determined by UV-visible spectroscopy. Beetroot, green tea, and flax seeds extract showed a satisfactory SPF value.

 Development of formulation

The cream formulation process involved melting stearic acid in a China dish at 85°C for the oil phase, while the aqueous phase was created by mixing potassium hydroxide, oleic acid, and water at the same temperature. The hot aqueous alkali solution was added to the oil phase with vigorous stirring while maintaining the heat throughout. As the mixture cooled, a creamy product was formed. F1, F2, F3, and F4 are different formulas for sunscreen bases. All four cream bases were compared, and F4 was chosen as the base formulation due to its physical appearance and buttery texture. Two portions of C1 and C2 creams (15 g each) were prepared, with 3 ml and 5 ml of beetroot, flax seed, and green tea extracts added, respectively. C2 cream with 5 ml of extracts exhibited greater stability and consistency than C1 cream with 3 ml of extracts. Based on observations and analysis, C2 cream was selected as the base for maximizing the SPF value after incorporating the herbal extracts. Figure 5 shows the formulated C1 and C2 creams.

 Physical parameters

The formulations’ appearance, color, and homogeneity were assessed, and the results are documented in Table 5 and Figure 5. It was determined that the two formulations (C1 and C2) demonstrated uniformity and homogeneity, with no observable variations after storage for one month as shown in Figure 6.

Subjective characteristics

The evaluations included the assessment of consistency, sensory attributes upon application, and the potential for skin irritation. The resulting data is recorded in Table 5. Notably, all formulations demonstrated favorable subjective characteristics, including consistent texture and absence of irritation upon application to the skin.

Spreadability

The ability of the formulated cream to spread evenly on the skin was assessed as an indicator of its efficacy. These findings were tabulated and are presented in Table 5, demonstrating the cream’s ability to spread uniformly for optimal application.

Thermal stability

The examination involved testing for oil separation from the cream under controlled conditions of 60%-70% relative humidity (RH). Two formulations were placed in a humidity chamber at 37 ± 1°C. Notably, no phase separation was observed, indicating that the formulations exhibited high thermal stability.

Evaluation of pH Levels

The pH of the creams was assessed to evaluate the potential for skin irritation resulting from acidic or alkaline pH levels. Acidic or alkaline pH levels may result in skin irritation, making this an important consideration^.22 The findings indicated that the creams generally exhibited a pH range of 6-7. This corresponds to the natural pH of human skin. Table 5 highlights the pH levels of two specific formulations within this range, suggesting they are well-suited for use on human skin. 

In-vitro determination of SPF

Aliquots were prepared to determine the SPF of the developed formulations. They were scanned between 290-320 nm, multiplying the resulting absorbance values by their respective EE (λ) and I (λ) values. The summation of these values was then corrected by a factor of 100. Both formulations C1 and C2 exhibited significant SPF values, as shown in Table 3. The SPF values of marketed synthetic formulations containing active sun protectant ingredients like butyl methoxy dibenzoyl methane, benzophenone-3, and titanium dioxide were lower than their label claims of 26.33 (Table 3). The formulated herbal sunscreens demonstrated an SPF of 34.54. 

Discussion

The developed herbal sunscreen formulations showed a higher SPF value than synthetic formulations in the market. Polyphenols, including betalain, lignans, flavonoids, and green tea, exhibited the highest SPF values. The formulated herbal sunscreens demonstrated good SPF values and synergistic action with excipients. They are gentle on the skin, environmentally friendly, and made from natural ingredients like plant extracts and essential oils. These sunscreens are free from harmful chemicals, reducing the risk of skin damage and allergies, and can be used on sensitive skin. The high antioxidant content helps protect against free radicals, prevents premature aging, tans, and sunburns, and reduces skin cancer risk.²³ Sunscreens mainly consist of synthetic and organic compounds, which enter the bloodstream after topical application, sparking concerns among the scientific community. As a result of the potential toxicity associated with synthetic molecules, researchers have turned their focus towards herbal formulations.²⁴ Herbal photo chemoprotective agents are preferred as they exhibit multifaceted mechanisms to mitigate skin cancer and photoaging.²⁵ Exposure to solar UV radiation can negatively impact human health. While synthetic sunscreen products have been employed as a preventative and therapeutic measure, their undesirable side effects led to an increasing emphasis on exploring alternative, plant-based formulations that are more human-friendly.²⁶

Conclusion 

UV radiation harms the skin; therefore, emphasis should be placed on proper sun protection. Through investigating the potential of herbal sunscreens containing beetroot, flax seeds, and green tea extracts, promising outcomes have been discovered regarding protection against sun damage. These formulations demonstrated significantly higher SPF values compared to synthetic options commonly available. By utilizing natural compounds such as betalains, flavonoids, and polyphenols, herbal sunscreens have proven effective in combatting the damaging effects of UV radiation. These formulations boast impressive SPF values and demonstrate thermal stability, spreadability, and appealing subjective characteristics. These herbal sunscreens are environmentally friendly and free of harmful chemicals, harnessing the power of plant extracts to offer skin protection without the potential risks associated with synthetic alternatives. Using natural compounds like betalains, flavonoids, and polyphenols, herbal sunscreens have effectively fought against the harmful impact of UV radiation.

Conflict of Interest

None