Comparative studies on sun protection factor of some sunscreen formulations used in cosmetics

Masheer Ahmed Khan* and Gajanand Engla

School of Pharmacy, Devi Ahilyavishwavidyalaya, Indore.

*Corresponding Author E-mail: masheerak@yahoo.com

ABSTRACT

The aim of this research was to determine sun protection factor (SPF) values of some sunscreen formulations used in cosmetics by ultraviolet spectrophotometer. Sun protection factor is a laboratory measure of the effectiveness of sunscreen, the higher the SPF, the more protection a sunscreen offers against the ultraviolet radiations causing sunburn. SPF is determined by spectrophotometric method reported by Mansur et al. Hydro alcoholic dilutions of oils were prepared and in vitro photo protective activity was studied by UV spectrophotometric method in the range of 290-320 nm. It was observed that the SPF values for cosmetic formulations were in between 13 and 16. Among the various sunscreen formulations SPF values were compared. The study is helpful in selection of sunscreens formulations used in cosmetics with better safety and high SPF values.

KEYWORDS: SPF, sun protection factor, sunscreens.

INTRODUCTION:

Sunscreens and sun blocks are chemicals that absorb or block UV rays and show a variety of immunosuppressive effects of sunlight. The use of skin care products specially sunscreens may be an effective approach for reducing UV-B-generated ROS-mediated photo-aging.^[1]Solar ultra violet radiations (UVR) are divided into three categories: UV-C (200-280 nm), UV-B (280-320 nm) and UV-A (320-400 nm). UV-C is the most biologically damaging radiation, but it is filtered out by ozone layer. Currently UV-B radiation and to a lesser extent UV-A radiation are responsible for inducing skin cancer. ^[2-4]

The efficacy of a sunscreen is usually expressed by the sun protection factor (SPF), which is defined as the UV energy required to produce a minimal erythemal dose (MED) in protected skin, divided by the UV energy required to produce an MED in unprotected skin.

SPF = Minimal Erythema dose in sunscreen-protected skin/Minimal Erythema 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.^[5]

The in vitro screening methods are advantagous as they may represent a fast and reasonable tool reducing the number of in vivo experiments and risks related to UV exposure of human subjects. There are two in vitro methods (measurement of absorption or the transmission of UV radiation through sunscreen product films in quartz plates or biomembranes and the absorption characteristics of the sunscreen agents are determined based on spectrophotometric analysis of dilute solutions).

The in vitro SPFs were determined according to the method described. The observed absorbance values at 5 nm intervals (290-320 nm) were calculated by using the formula

SPF_{spectrophootmetric} = CF x ₂₉₀∑³²⁰ EE_(λ) x I x Abs_(λ)

Where, CF = correction factor (10), EE (_λ) = erythmogenic effect of radiation with wavelength λ, Abs (_λ) = spectro photometric absorbance values at wavelength λ. The values of EE x I are constants. They were determined by Sayre et al and are given in Table 1.

Table 1: Values of EE x I at different wavelength

Wavelength	Value of EE x I
290	0.0150
295	0.0817
300	0.2874
305	0.3278
310	0.1864
315	0.0837
320	0.0180

However, there are many factors affecting the determination of SPF values, like the use of different solvents in which the sunscreens are dissolved; the combination and concentration of the sunscreens; the type of emulsion; the effects and interactions of vehicle components, the interaction of the vehicle with the skin; the addition of other active ingredients; the pH system and the emulsion rheological properties, which can increase or decrease UV absorption of each sunscreen. The effect that different solvents and emollients have upon the wavelength of maximum absorbance, alone or in combination, is reported in several studies ^[6-11]

Vehicles used for sunscreens formulations are hydroalcoholic lotions, water-in-oil or oil-in-water emulsions and oily lotions. The sunscreening preparation must spread on the skin, should remain in place as a continuous film, should closely adhere to the surface and should resist washing off by perspiration. Standard techniques for spectrophotometric evaluation of sunscreens preparations involve solution of a known weight of the screen or preparation in an ultraviolet transparent solvent.^[12]

MATERIALS AND METHODS:

Sunscreen formulations of various manufacturers were purchased from local retailers. The maximum solubility was observed in 40% ethanol and 60% distilled water solution. Ethanol (Merck^®) of analytical grade was used for preparation of stock and sample solutions.

Initial stock solution was prepared by taking 1% w/v of cream/lotion in ethanol and water solution (40:60). Then from this stock solution, 200g/ml dilution was prepared. Thereafter, absorbance values of each formulation (F₁, F₂ & F₃) were determined from 290 to 320 nm, at 5-nm intervals, taking 40% ethanol and 60% distilled water solution as blank, using Shimadzu UV-Visible spectrophotometer (Shimadzu 1700, Japan).

Sun protection Factor determination

The absorbance values of different formulations were taken between 290 and 320 nm, and the obtained absorbance values were multiplied with the respective EE _(λ) values. Then, their summation was taken and multiplied with the correction factor (10).

RESULTS AND DISCUSSION:

The effectiveness of a sunscreen formulation was illustrated in terms of SPF (sun protection factor). The SPF of different formulations (F₁, F₂& F₃) was determined using UV spectrophotometric analysis and are shown in table 2. The SPF values of different formulations range between 10.59 to 16.72. The maximum SPF was observed in formulation F₁.

The SPF values of different formulations were compared with the reported values and found in proximity. Thus the present studies helps in the selection of sunscreen formulations which is more effective in preventing the sunburns.

Table2: Absorbance of sunscreen formulations.

Wavelength (nm)	EE_(λ)Employed	Formulation 1 (F₁)	Formulation 2 (F₂)	Formulation 3 (F₃)
290	0.0150	0.016	0.076	0.061
295	0.0817	0.118	0.094	0.091
300	0.2874	0.301	0.231	0.118
305	0.3278	0.533	0.399	0.631
310	0.1864	1.646	0.613	0.864
315	0.0837	1.373	0.936	0.929
320	0.0180	1.147	0.775	0.694

Thus to develop sunscreens with better safety and high SPF, the formulator must understand the physicochemical principle, not only the UV absorbance of the actives but also vehicle components, such as esters, emollients, emulsifiers and fragrances used in the formulation, since sunscreens can interact with other components of the vehicle, and these interactions can affect the efficacy of sunscreens.

CONCLUSION:

The present study examines the SPF (sun protection factor) values of different formulations using UV spectrophotometric method which is simple, rapid, economic and can be useful in the determination of SPF values of other cosmetic formulations too. The proposed methodology may also be useful as a rapid quality-control method for the sunscreen formulations. Therefore the knowledge of SPF values will be a major tool in the selection of the various sunscreen formulations.

ACKNOWLEDGMENTS:

The authors are thankful to University Institute of Pharmacy, Pt. R. S. Shukla University, Raipur (CG), for providing necessary facilities for the studies.

REFERENCES:

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Received on 02.12.2012 Accepted on 21.12.2012

Res. J. Topical and Cosmetic Sci. 3(1): July-Dec. 2012 page 34-36

Name of formulation	SPF Values
F₁	16.72
F₂	10.59
F₃	11.71