FACTORS AFFECTING SPF AND PA VALUES OF SUNSCREEN CREAM FORMULATIONS 149 in Table I. The response parameters are calculated SPF and PA values as well as texture profi les of the developed formulations. Formulations and preparation of sunscreen products. The ingredients of sunscreen formulations (F1–F8) in Table II were prepared based on a 23 factorial design layout shown in Table III. The center point of each factor was presented in F9. The oil phase containing octylmeth- ylcinnamate, titanium dioxide (and) diethylhexyl carbonate (and) polyglyceryl-6 polyhy- droxystearate, light mineral oil, stearic acid, C12-15 alkyl benzoate (and) dipropylene glycol dibenzoate (and) PPG-15 stearyl ether benzoate, Span 80, and butylated hydroxy toluene were mixed and heated in a water bath to 70°C. The water phase containing Table I Factorial Design Parameters and Experimental Conditions Factors Levels Low (−) High (+) (A) Phase volume ratio (oil:water) 25:75 30:70 (B) Xanthan gum 0% 0.30% (C) Stearic acid 3% 5% Table II Ingredients of Sunscreen Formulations Based on 23 Factorial Design F1 F2 F3 F4 F5 F6 F7 F8 F9 Octylmethoxycinnamate 7 7 7 7 7 7 7 7 7 Titanium dioxide (and) diethylhexyl carbonate (and) polyglyceryl-6 polyhydroxystearate 10 10 10 10 10 10 10 10 10 Mineral oil 2.5 7.5 2.5 7.5 0.5 5.5 0.5 5.5 4 Stearic acid 3 3 3 3 5 5 5 5 4 C12-15 alkyl benzoate (and) dipropylene glycol dibenzoate (and) PPG-15 stearyl ether benzoate 2 2 2 2 2 2 2 2 2 Vitamin E acetate 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Span 80 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Propylene glycol 3 3 3 3 3 3 3 3 3 Cabopol 940 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Xanthan gum — — 0.3 0.3 — — 0.3 0.3 0.15 Triethanolamine 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 BHT 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 EDTA 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Tween 80 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Propylene glycol (and) diazolidinyl urea (and) methylparaben (and) propylparaben 1 1 1 1 1 1 1 1 1 Purifi ed Water qs to 100 100 100 100 100 100 100 100 100

JOURNAL OF COSMETIC SCIENCE 150 propylene glycol, carbopol 940, xanthan gum, EDTA (tetra sodium), Tween 80, and de- ionized water were mixed well before adding triethanolamine. The water phase mixture was then heated in water bath to 75°C and poured into the oil phase mixture. After that, the emulsion mixture was continuously stirred until the temperature reached 45°C. Then, vitamin E acetate, propylene glycol, diazolidinyl urea, methylparaben, and propyl- paraben were added and homogenized for 5 min. Determination of in vitro SPF and PA values. An opened window in thick plastic with a dimension of 0.8 × 2 cm2 was made as a sample holder. Transpore® tape of size 1.2 × 3 cm2, which was taped one-side with transparent tape, was used as a sample plate. Sun- screen products, 2 mg/cm2, were applied evenly on the whole surface of the rough side of the sample plate. After weighing, the sample was spread using light circular strokes over the whole surface of the plate and allowed to dry for 15 min at room temperature. Seven plates were prepared for each tested sample. The transmittance of UV in a range of 290– 400 nm through the sample plate was measured against a blank plate using UV-visible spectrophotometer UV-17000 PharmaSpec (Shimazu, Japan). Determination of SPF according to the method of Diffey and Robson (6) In vitro SPF was calculated as in equation (1): λ λ λ λ ‰ ‰ œ œ 400 290 400 290 SPF /Tλ E In vitro E (1), where E(λ) is the spectral irradiance of the used light spectrum at wavelength λ nm, ∈(λ) is the erythemal action spectrum at wavelength λ nm corresponding to the International Commission on Illumination (CIE) publication (23), and T(λ) is the spectral transmit- tance of the sunscreen. The calculated SPF values were obtained from equation (1). A corrected SPF value for samples was determined using a linear regression equation plotted between the label SPF values of SPF 4.47 and SPF 15 as well as the labeled SPF and PA values of the international Table III 23 Factorial Design Layout Combination Formulation Composition A B C (1) F1 − − − A F2 + − − B F3 − + − AB F4 + + − C F5 − − + AC F6 + − + BC F7 − + + ABC F8 + + + F9 0 0 0