INTRODUCTION:

Sunlight is a portion of electromagnetic radiation given off by the sun, in particular infrared, visible and ultraviolet light. Solar radiation is recognized to have negative effects on human skin on exposure. Out of all ultraviolet light is the most deleterious to the skin and sunburns are caused, ageing of skin and over the long term, skin cancer⁴.

Sun emits UV radiation with radiation spectrum of 200nm to 400nm. This can be divided three regions: UVA [from 320nm to 400nm], UVB [from 290nm to 320nm], UVC [from 200nm to 290nm]^2,3,4,7.

UVC radiation is filtered by the atmosphere prior reaching to the earth. UVB radiation is not entirely filtered out through the ozone layer and that leads to damage due to sunburn. UVA radiation reaches the deeper layers of the epidermis and dermis and induce the premature aging of the skin. UV radiation have been inculpated as a causative factor of skin cancer⁶.

Repeated sun exposure increases the risk of three types of cancer: melanoma, basal cell carcinoma, and squamous cell carcinoma with melanomas causing higher mortality while the non- melanoma skin cancers are associated with higher morbidity and aesthetic skin damage. Different clinical studies have shown that regular use of sunscreens can promote skin cancer reduction, especially melanoma and squamous cell carcinoma⁸.

The use of sunscreens as photo-protectants has evolved significantly over the last few decades. With increasing awareness of the protection afforded by sunscreens against sunburns, skin aging and melanomas, the demand for sunscreen formulations invariably increased, and there exists a significant opportunity for pharmaceutical industries to fulfil this demand by manufacturing quality, efficacious, safe and aesthetically appealing sunscreen formulations. Commonly used cosmetics are sunscreens. These are formulations that are applied onto the skin surface to protect it from the harmful effects of ultraviolet (UV) light⁹.

Sunscreen also known as sunblock lotion or suntan lotion is a lotion, spray, gel, or other tropical product that provides a protective layer to the skin that prevents UV-rays to reach the skin either by absorbing or by reflecting them.

Sun protection factor:

Sunscreens have an individual sun protection factor (SPF), value that is defined as the ratio of the minimal erythemal dose on sunscreen protected skin (MEDp) to the minimal erythemal dose on unprotected skin (MEDu), as showed on Equation^1,2,3,4.

Minimal eryyhema a dose in sunscreen ptotected skin

SPF = --------------------------------------------------------------

Minimal erythema a dose in nonsunscreen protected skin

The minimal erythemal dose (MED) is defined as the lowest time interval or dosage of UV light irradiation sufficient to produce a minimal, perceptible erythema on unprotected skin. The higher the SPF, the more effective is the product in preventing sunburn. Nevertheless, it is necessary to standardize methods to determine the SPF of these products. The photoprotection afforded by topical sunscreens against solar ultraviolet radiation exposure can be determined in vivo or in vitro, and it is ideally determined by photo- testing in human volunteers. This type of determination has been used for many years and although useful and precise, is a time- consuming process, complex and expensive, particularly when information concerning to the protection against long wavelength (UVA) is required. As a consequence, much effort has been devoted to the development of in vitro techniques for assessing the photoprotection of sunscreen compounds^2,3,4.

The methods in vitro are in general of two types. Methods which involve the measurement of absorption or the transmission of UV radiation through sunscreen product films in quartz plates or bio-membranes, and methods in which the absorption characteristics of the sunscreen’s agents are determined based on spectrophotometric analysis of dilute solutions^2,3.

Mansur et al developed a very simple mathematical equation which substitutes the in vitro method proposed by Sayre et al, utilizing UV spectrophotometry and the following equation^2-5.

Where: EE (l) – erythemal effect spectrum; I (l) – solar intensity spectrum; Abs (l)- absorbance of sunscreen product; CF – correction factor (= 10). It was determined so that a standard sunscreen formulation containing 8% homosalate presented a SPF value of 4, determined by UV spectrophotometry.

The values of EE×I are constants. They were determined by Sayre et al., are shown in Table 1^2,4,5.

Table 1: Normalized Product Functions Used in The Calculation Of SPF.

Wavelength λ(nm)	EE×I(normalized)
290	0.0150
295	0.0817
300	0.2874
305	0.3278
310	0.1864
315	0.0839
320	0.0180
Total	1

EE- erythemal effect spectrum, I – solar intensity spectrum

MATERIAL AND METHODS:

Materials:

Reagent: Analytical grade ethanol.

Samples: commercially available sunscreens of eight different brands with different SPF were purchased from the local store and in pharmacies.

Instrumentation: A double beam Shimadzu UV- Vis Spectrophotometer with 1cm quartz cuvettes is used for absorbance measurement.

Methods:

Ⅰ Determination of SPF values of various brand sunscreens with different SPF values.

Sample preparation:

About 1.0gm of sample was weighed and transferred in a 100ml volumetric flask, analytical grade ethanol about 3/4^thvolume was added. The contents were stirred for about 10 minutes and made up to the mark using analytical grade ethanol. The solution was filtered through Whatman No 1 filter paper and the filtrate was collected by rejecting the first few ml of the filtrate. 5ml of the aliquot was taken in a 50ml volumetric flask and made up to the mark using analytical grade ethanol. The 5ml of the diluted solution was taken in to the 25 ml volumetric flask and made up to the mark using analytical grade ethanol. Then the same procedure is followed for the rest of the samples, totally five samples (A, B, C, D, E) are prepared^2,4.

Measurement of UV absorption:

After preparation, all the samples were scanned at wavelength between 290 and 320nm, in the range of UVB, every 5nm. At the end of all measurements, the Mansur equation was applied to calculate SPF values^2,3,4.

Ⅱ Comparison of different brand sunscreens same SPF (30).

Commercially available sunscreens of four different brands with same SPF 30 were prepared as samples by above mentioned procedure and measurement of UV absorption is done and the absorbance values were compared¹⁰.

RESULT:

ⅠSPF values determination:

The determination of SPF values for all five samples were made through the UV spectrophotometric method and the Mansur equation was applied. The results are shown in Table 2.

Table 2: values of SPF labelled and SPF found on five samples.

Sample	Labelled SPF	Found SPF	(Found SPF/ Labelled SPF) ×100
Sample A	15	12.21	81.4%
Sample B	20	16.22	81.1%
Sample C	30	25.62	85.4%
Sample D	40	32.09	80.22%
Sample E	50	25.89	51.78%

Ⅱ Comparison of SPF values:

The comparison of SPF values for all four samples we made through the UV spectrophotometric method and the Mansur equation was applied. The results are shown in Table 3.

Table 3: Comparison of SPF values of four different brands.

Sample	Labelled SPF	Found SPF	(Found SPF / Labelled SPF) ×100
Sample 1	30	25.62	85.4%
Sample 2	30	25.89	86.3%
Sample 3	30	18.77	62.56%
Sample 4	30	14.04	46.8%

Among the samples (1, 2, 3 and 4) analysed, sample 2 exhibits the highest absorbance value, considering the corresponding SPF labelled. This sample’s found SPF corresponds to 86.3% when compared to the labelled SPF whereas, sample 4 exhibits the least absorbance value and this sample’s found SPF corresponds to 46.8%.

From the above comparison, we conclude that the; sample 2 > sample 1 > sample 3 > sample 4

DISCUSSION:

The SPF value of five different commercially available products results are shown in table along with the information related to the presence of active ingredient, labelled SPF value and the difference between the labelled SPF and the observed value⁵.

From the table-4 it was observed that sample A, B, C, D and E shows closer agreement between the labelled SPF value and the observed SPF value. The differences between the labelled and observed SPF values are 2.79, 3.78, 4.38, 4.11 and 11.23 respectively⁵.

Table 4: Difference in observed SPF from labelled SPF.

Sr.no	Sample	Active ingredients	labelled SPF	Observed SPF	Difference
1	Sample A (SPF 15)	Zinc oxide, ascorbic acid, sodium riboflavin phosphate	15	12.21	2.79
2	Sample B (SPF 20)	Zinc oxide, Ascorbic acid	20	16.22	3.78
3	Sample C (SPF 30)	Octyl methoxy cinnamate, Butyl methoxydibenzoylmethane, cyclopantasiloxane	30	25.62	4.38
4	Sample D (SPF 40)	Octyl methoxy cinnamate, Butyl methoxydibenzoylmethane, cyclopantasiloxane	40	32.09	7.91
5	Sample E (SPF 50)	Polyhydroxystearic acid, Neopentyl glycol diheptanoate, cetostearyl alcohol	50	25.89	24.11

Table 5: Difference in observed SPF and labelled SPF.

Sr.no	Sample	Active ingredients	Labelled SPF	Observed SPF	Difference
1	Sample 1 (SPF 30)	Octyl methoxy cinnamate, Butyl methoxydibenzoylmethane, cyclopantasiloxane	30	25.62	4.38
2	Sample 2 (SPF 30)	Ethylhexyl Methoxycinnamate, Butyl methoxydibenzoylmethane	30	25.89	4.11
3	Sample 3 (SPF 30)	Aloe barbadensis, Triticum sativum, Cocos nucifera	30	18.77	11.23
4	Sample 4 (SPF 30)	Phenylbenzimidazole sulfonic acid, Disodium phenyl dibenzimidazole tetra sulfonate, Ethylhexyl methoxycinnamate	30	14.04	15.96

From the above table it is observed that sample 1, 2, 3 and 4 shows closer agreement between the labelled SPF value and the observed SPF value. The differences between the labelled and observed SPF values are 4.38, 4.11, 11.23 and 15.96 respectively.

These data variations can be due to the various reasons like the type of emulsion used for the formulations, the effects and interactions of vehicle components, the pH system and the emulsion rheological properties, use of different solvents in which the sunscreens are dissolved etc., can increase or decrease UV absorption of each sunscreen. Excipients and other active ingredients can also produce UV absorption bands, thus interfering with those of UVA and UVB sunscreen. The effect that different solvents and emollients have upon the wavelength of maximum absorbance and upon the UV absorbance of several sunscreens chemical alone or in combination is well known and documented.

Hence before studying the SPF value of sunscreen products by in-vitro method, scientist should understand not only the UV absorbance of the actives, but also vehicle components, such as esters, emollients and emulsifiers used in the formulation.

ACKNOWLEDGMENTS:

The authors wish to thank Department of Pharmaceutical Analysis, TVM College of Pharmacy for supporting this study.

REFERENCE:

1. Kiriiri Geoffrey, A.N. Mwangi, S.M. Maru, et al. Sunscreen products: Rationale for use, formulation development and regulatory considerations, Saudi Pharmaceutical Journal .1012- 1013.

2. Elizangela Abreu Dutra, et al. Determination of sun protection factor (SPF) of sunscreens by ultraviolet spectrophotometry, Brazilian Journal of Pharmaceutical Sciences. Vol. 40, N. 3, Jul./Sept., 2004, 381-382.

3. Fonseca AP and Rafaela N, Determination of Sun Protection Factor by UV-Vis Spectrophotometry, Instituto Politecnico de Coimbra, ESTESC, D Farm, GIAF, Rua 5 de Outubro S. Martinho do Bispo Apartado 7006, 3040-854.

4. Vijayaraghavan Sudhahar and Vadivelu Balasubramanian, Sun production factor (SPF) determination of marketed sunscreen formulation by In-Vitro method using UV-VIS spectrophotometer, Scholars Research Library,119-122.

5. Mbanga L, Mpiana PT, Mumbwa AM, Bokolo K, Mvingu K, et al. (2014) Determination of Sun Protection Factor (SPF) of Some Body Creams and Lotions Marketed in Kinshasa by Ultraviolet Spectrophotometry. J Phys Chem Sci 2: 1.

6. P Balasaraswathy, Udaya Kumar, CR Srinivas, Shashidharan Nair (2002) UVA and UVB in sunlight, Optimal Utilization of UV rays in Sunlight for phototherapy Indian Journal of Dermatology, Venereology, and Leprology Department of Dermatology, PSG Institute of Medical Science and Research, Peelamede, Coimbatore, India2 Department of Physics, PSG Institute of Technology, Coimbatore, India.

7. David Welch, Manuela Buonanno, Veljko Grilj, Igor Shuryak, Connor Crickmore, Alan W. Bigelow, et al., (2018) Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases.

8. Zoe Apalla, Dorothée Nashan, Richard B. Weller and Xavier Castellsagué, (2017), Skin Cancer: Epidemiology, Disease Burden, Pathophysiology, Diagnosis, and Therapeutic Approaches.

9. Sharad P. Paul, (2019), Ensuring the Safety of Sunscreens, and Their Efficacy in Preventing Skin Cancers: Challenges and Controversies for Clinicians, Formulators, and Regulators.

10. Syring F, Weigmann H.-J, Schanzer S, Meinke M.C, Knorr F et al., (2006) Investigation of Model Sunscreen Formulations Comparing the Sun Protection Factor, the Universal Sun Protection Factor and the Radical Formation Ratio, Skin Pharmacology and Physiology.

Received on 13.09.2021 Modified on 24.11.2021

Asian J. Pharm. Ana. 2022; 12(2):111-114.

DOI: 10.52711/2231-5675.2022.00020