J. Cosmet. Sci., 67, 101–108 (March/April 2016) 101 A new in vitro method to determine sun protection factor XIN QU, XIAOMIN ZHAO, and ZHIHUA CHEN, ASI Shanghai Technical Center, Ashland Inc., Shanghai, China 200233. Accepted for publication April 17, 2016. Synopsis A new in vitro sun protection factor (SPF) test method to determine the effi cacy of sun care products is proposed and evaluated. Based on ultraviolet (UV) dose cumulate response protocols, the new method employs Gafchromic EBT3 fi lm, a self-developing dosimetry fi lm originally created for applications in radiotherapy. Unlike the current standardized method, a UV spectrophotometer is not required. In vitro SPF values of 15 commercial products were measured with EBT3 fi lm and compared with labeled in vivo SPF values. It is apparent that the new method is accurate, cost-effective, and reproducible. These results can be seen across sun care product lines, including sunscreen lotions, blemish balm (BB) creams, foundations, and sprays with organic and/or inorganic UV fi lters. INTRODUCTION Determining the effi ciency of sun care products is normally assessed in accordance with a long-established, standardized in vivo sun protection factor (SPF) test (1). This test uti- lizes minimal erythema dose (MED), defi ned as the minimum dose or time of radiation that produces skin erythema, to determine SPF, the dose (MED), or time of UV radiation required to cause sunburn/erythema on skin with sunscreen on, as a multiple of the dose or time required without sunscreen (equation 1). For example, if unprotected skin has a dose to erythema (40 J) and protected skin has dose to erythema (640 J), then SPF = 640/40 = 16. An SPF equal to 1 affords no UV protection. Dosage with sunscreen SPF= Dosage without sunscreen MED MED (1) The more commonly used standard nowadays, the in vitro SPF test method, dates back to the early 1990s and is based on the measurement of spectral transmittance of sunscreen applied to a transparent substrate material (2). Specifi cally, transmittance of sunscreen is the ratio of spectral transmittance through a defi ned amount of sunscreen applied. The measured spectral power distribution is then weighted by the defi ned solar spectrum and Address all correspondence to emascari@resourceadvantage.com.

JOURNAL OF COSMETIC SCIENCE 102 erythemal effectiveness functions to yield the calculated in vitro SPF. The in vitro SPF is calculated as follows: λ λ λ λ λ λ λ λ 0 = 400 nm = 290 nm = 400 nm –A ( ) = 290 nm ( ) × SPF= ( ) × ( ) × × dλ E Idλ×)λ( E I10 ෾ ෾ (2) where E (λ) = erythema action spectrum (CIE-1987), I (λ) = spectral irradiance of the UV source (SSR or SPF testing), A0 (λ) = mean monochromatic absorbance measurements per plate of the test product layer before UV exposure, and dλ = wavelength step (1 nm). Each test method has its advantages and drawbacks. The in vivo SPF test is based on a biological endpoint (skin erythema/sunburn) and affords a UV dose cumulate response. This method is similar to real sunscreen applications, but it is expensive, time consum- ing, and affected by skin types. It is also subjective due to reliance on human observation of skin erythema. On the other hand, in vitro SPF testing is objective, cheap, and fast, with no requirement of human observation however, it is based on UV spectral transmit- tance measurements and has no UV dose cumulating response. Accordingly, a number of parameters will affect the results, such as substrate materials, roughness, amount of sun- screen applied, and sunscreen photostability (3,4). Given these variables, the in vivo SPF test is still required by all countries and regions that regulate commercial sunscreen products with SPF label claims. In the following experiments, a new in vitro SPF test based on UV dose cumulate response is examined with Gafchromic EBT3 fi lm (Ashland, Bridgewater, NJ). EBT3 fi lm has been developed to address the needs of the medical physicist and dosimetrist working in a radiotherapy environment (5). It is sensitive to UV, but not typically to visible light. The color of EBT3 fi lm changes from green to dark under cumulative UV irradiation (6). The effective atomic number (Zeff) of this fi lm is 6.8, a value close to human skin (Zeff = 7.4), while Zeff is defi ned as the nature of radiation interaction with the medium. EXPERIMENTAL MATERIALS A total of 15 commercial sunscreen lotions, BB creams, foundations, and sprays with organic and/or inorganic UV fi lters were purchased from the market. In addition, two sunscreen standards required for in vitro SPF testing were purchased from Cosmetech Laboratories Inc., Fairfi eld, NJ. The Q-SUN test chamber (Q-lab, Westlake, OH), irra- diation inten sity 41 w/m2, and temperature of 40oC were used to irradiate Gafchromic EBT3 fi lm. The color change of the fi lm was scanned using an Epson 4990 scanner (Long Beach, CA) and analyzed by FilmQA pro software (Ashland) to establish the calibration curve. METHODS EBT3 fi lm was cut to a rectangular shape (5.1 × 6.3 cm), irradiated in the Q-SUN chamber with different time periods and scanned using the Epson 4990. The absorbed radiation