JOURNAL OF COSMETIC SCIENCE 150 (3) Key West, FL (4) and the Virgin Islands (5) in the United States have banned two monographed organic UV fi lters, namely, oxybenzone [International Nomenclature of Cosmetic Ingredients (INCI) benzophenone-3] and octinoxate (INCI: ethylhexyl methoxycin- namate) because of their harmful environmental effects (6). The United States has a low num- ber of UV fi lters to start with and the over-the-counter (OTC) monograph restricts certain combinations. Now, with the bans, sunscreen formulators in the United States have a very limited selection of organic UV fi lters they can incorporate into sunscreen products, and it is challenging to achieve a reasonably high SPF and broad-spectrum protection. The need for SPF and broad-spectrum protection boosting technologies is greater than ever. For an organic UV fi lter to be an effective sunscreen, it must be soluble in at least a por- tion of the sunscreen formulation (7). Therefore, solvents play an essential role in the performance of sunscreens. Traditionally, octanol–water partition coeffi cient (logP) was used as an indication of lipophilicity and solubility. A newer approach is to use Hansen solubility parameters (HSPs), which are more versatile and look at solubility from a more complex approach (8). Each ingredient has three HSPs, δD for dispersion, δP for polarity, and δH for hydrogen bonding, which defi ne its location in a three-dimensional space, the HSP space. HSP is based on the theory of “like dissolves like.” Ingredients with similar HSPs dissolve well in each other, whereas dissimilar HSP values indicate that two ingre- dients will not mix/dissolve in each other. Formulating for Effi cacy™ (FFE, ACT Solutions Corp., Newark, DE) is a computer program that matches active and inactive ingredients based on their HSPs (9). In addition to matching ingredients, FFE also calculates the ingredient active gap (IAG). IAG refers to the similarity of the ingredient and active ingredient (i.e., solvent and UV fi lter in this study). In general, the smaller the IAG, the more alike the active and solvent, and as “like dissolves like,” the solubility will be higher. HSPs and IAG are applied in many sectors, including pharmaceuticals (10,11), personal care products (12), polymers (13–15), and paints and coatings (16,17). Using HSPs and IAG allows for a logical and streamlined selection process, which can save time and money for formulators. Solve nts often have different labels on supplier datasheets, including emollient, photosta- bilizer, and SPF booster. The current trend is to achieve a high SPF with only small amounts of UV fi lters because of economical, ecological, sensorial, and health-related reasons (7). A way to achieve this goal is to incorporate ingredients in the formulation that can attain better UV performance with less UV fi lters. Solvents have an important role in dissolving UV fi lters and contributing to the aesthetics of the product. In addition, certain emol- lients have been found to contain the properties of UV fi lters and, therefore, impart an SPF of their own (18). Solvent polarity was also found to affect the wavelength of maxi- mum absorbance (λmax) and critical wavelength in sunscreen formulations (19). In this project, our goal was to evaluate the effect of 24 solvents on the in vitro SPF, λmax, and broad-spectrum protection (i.e., critical wavelength) of three organic UV fi lters and a blend of these three UV fi lters. Solvent selection was based on a modern approach, i.e., IAG calculated by FFE. MATERIA LS UV fi lt ers included avobenzone [INCI: butyl methoxydibenzoylmethane (BMDM), United States Adopted Name (USAN): avobenzone] and homosalate (INCI/USAN: homosalate) purchased from Making Cosmetics (Redmond, WA), and Neo Heliopan OS® (INCI: ethyl- hexyl salicylate, USAN: octisalate) provided by Symrise (Elyria, OH). Today, the most widely

SOLVENT EFFECTS ON SPF AND BROAD-SPECTRUM PROTECTION 151 used UVB fi lters in the United States include benzophenone-3, octocrylene, homosalate, and ethylhexyl salicylate (7). Because of the aforementioned bans, we only selected the “coral-safe” UVB fi lters to study. Butyl methoxydibenzoylmethane is one of the most effi cient UVA- absorbing fi lters used around the globe, and it is the only UVA-absorbing organic fi lter approved in the United States. Because no single UV fi lter is capable of providing a high SPF and broad-spectrum protection, the combination of the three fi lters was tested as well. Solvents selected by FFE included isododecane and cyclomethicone (INCI: cyclotetrasi- loxane and cyclopentasiloxane) purchased from Making Cosmetics SymMollient PDCC® (INCI: propanediol dicaprylate/caprate), Corapan TQ® (INCI: diethylhexyl 2,6-naph- thalate), and Hydrolite 5® (INCI: pentylene glycol) provided by Symrise Crodamol SFX® (INCI: PPG-3 benzyl ether ethylhexanoate), Cromollient ESP® (INCI: tris(PPG-3 benzyl ether) citrate), and super-refi ned castor oil provided by Croda (Mill Hall, PA) Kollicream IPM® (INCI: isopropyl myristate) and Myritol 318® (INCI: caprylic/capric triglyceride) provided by BASF (Florham Park, NJ) Eastman GEM® (INCI: 2-ethylhexyl palmitate) provided by Eastman (Miami, FL) AC Olive Oil Clear® [INCI: Olea europaea (olive) fruit oil] provided by Active Concepts (Lincolnton, NC) Finsolv TN® (INCI: C12-15 alkyl benzoate) provided by Innospec (Houston, TX) Lipex Shealight® (INCI: shea butter ethyl esters) provided by AAK (Karlshamn, Sweden) mineral oil (INCI: mineral oil) purchased from The Personal Formulator (Evanston, WY) sunfl ower seed oil [INCI: Helianthus annuus (sunfl ower) seed oil] purchased from Spectrum Chemical (New Brunswick, NJ) Schercemol 318® (INCI: isopropyl isostearate) provided by Lubrizol (Wickliffe, OH) LexFeel Natural® (INCI: heptyl undecylenate) provided by INOLEX (Philadelphia, PA) Hallbrite BHB® (INCI: butyloctyl salicylate), Hallstar DIPA® (INCI: diisopropyl adipate), SolaStay S1® (INCI: ethylhexyl methoxycrylene), and Polycrylene® (INCI: poly- ester-8) provided by Hallstar (Chicago, IL) Belsil DM 10® (INCI: dimethicone) provided by Wacker Chemie (Adrian, MI) and ethanol purchased from Decon Laboratories Inc. (King of Prussia, PA). METHODOLOGY FFE™ A search was made on UL Pro spector for a list of emollients commonly used as solvents for UV fi lters. The keywords used in the search included “sunscreen solvent,” “sunscreen solubilizer,” “sunscreen photostabilizer,” and “UV fi lter solvent.” Boosters are usually defi ned as ingredients that can signifi cantly increase the SPF without meaningfully contributing to SPF. Photostabilizers are molecules that can reduce or avoid the photodegradation of UV fi lters. Solvents are liquids used to dissolve ingredients in products, provide a vehicle for formulations, and also contribute to the texture of products. The same ingredient can often fulfi ll multiple functions. For example, photostabilizers often boost the overall SPF by preventing the UV fi lter from degradation, which makes them multifunctional ingre- dients. For simplicity purposes, we called all the ingredients screened and then selected for testing solvents. The UL Prospector search re sulted in 102 solvents. The solvents were entered into FFE us- ing their canonical simplifi ed molecular-input line-entry system (SMILES). Based on the SMILES, HSPs were generated and IAG was calculated. With FFE’s own default solvents,