More than three years ago, the FDA introduced a proposed rule that includes testing of sunscreen efficacy in vivo (SPF and UVA-PF) and in vitro (UVAI/UV ratio after pre-irradiation).1 The FDA requires U.S. sunscreen manufacturers to declare, in addition to SPF, the level of UVA protection provided by sunscreen product, based on the lowest result obtained using in vivo and in vitro UVA testing.
The FDA’s vision is to ensure and reward balanced and photostable UVA/UVB protection; according to the agency, both UVB and UVA radiation protection are equally important and more protection against UVA radiation damage is beneficial for consumers’ health. Others, however, have questioned the use of high SPF products.2
FDA also indicates its position regarding sunscreens with high SPF values. Data submitted to FDA show that the SPF test is accurate and reproducible for sunscreens with SPF up to 50. Thus, the agency proposes to allow labeled SPF values up to 50+ for the following reasons: to satisfy consumers who desire or need high levels of UV protection; help to compensate for inadequate application and/or re-application; provide additional sunburn protection during intense UV radiation conditions; help reduce cumulative UV radiation exposure; and generally provide consumers with incremental increases in sunburn protection.
FDA recognizes that future data may demonstrate that test variability may not be a problem for sunscreen products over SPF 50. It states that it will consider specific SPF values greater than 50 upon receipt of data demonstrating that accurate and reproducible results can be obtained from the SPF test for sunscreen products with SPF values over 50. According to FDA, allowing manufacturers to label sunscreens as “SPF 50+” may encourage further research into skin photobiology and the development of effective and safe sunscreen drug products with specific SPF values over 50.
Apparently, major U.S. sunscreen manufacturers followed this FDA encouragement by developing numerous commercial sunscreen products with SPF label values ranging from 100 to 110, which numerically are at least two times higher than the proposed limit of SPF 50+; all these products were introduced to the market in 2010 with description “new” on the packages.
From the technical point of view, the development of sunscreen products with 100+ SPF values using sunscreen actives selected from the current FDA approved list is a challenging task that requires creativity and utilization of optimized delivery systems in conjunction with:
• Photostabilizing technologies and ingredients, for example Helioplex,3 Avo- triplex,4 triplet combination of avobenzone, octocrylene and oxybenzone,5 and the use of sufficient levels of octocrylene to photostabilize avobenzone, etc.;
• SPF boosting technologies and ingredients, diethylhexyl syringylidenemalo- nate,6 styrene/acrylates copolymer microspheres,7 Triplet-Triplet and Singlet-Singlet quenchers8 and UV attenuating emollient butyloctyl salicylate;and
• Utilization of effective film-forming polymers, antioxidants, plant-derived ingredients and additional particulates (silica, modified silica) that help to improve overall product efficacy, sensorial profile and generate additional skin benefits.
Absorbance Spectra of Commercial SPF 100+ sunscreen products after pre-Irradiation
Materials and Methods
Eight commercially available sunscreen products with label SPF waterproof (very water resistant) values ranging from SPF 100 to 110 are shown in the photo below. These products were evaluated in vitro according to the FDA proposed rule using Vitro Skin (N-19)9 as alternative substrate instead of roughened quartz plates, which FDA proposed for the in vitro portion of its UVA test method while requesting comments regarding the suitability of other possible substrates. The suitability of Vitro Skin (N-19) as an alternative substrate for evaluation of UVAI/UV ratio was demonstrated by Dueva-Koganov et al.10
Commercially available SPF 100+ sunscreen products
The diffuse transmittance/absorbance measurements were conducted on the transmittance analyzer with integrated sphereLabsphere UV 2000S with Version 1.2 software to measure FDA proposed UVAI/ UV ratio.13 Pre-irradiation dose for each test product was calculated based on its actual SPF label value according to the formula: SPF 1 MED 2/3, where 1 MED = 200 J/m2-erythemally effective dose. Absorbance spectra of all test articles were within the dynamic range for Labsphere UV 2000S.13
Measurements of the contact angle of water to quantify the effects of test products on the surface properties of a skin-substitute substrate Vitro Skin (N-19) were conducted according to the test methodology described in a paper by Dueva-Koganov et al.14 where it was demonstrated that products producing relatively low contact angles tend to make more “light” and “non-greasy” sensory claims, while products that produce relatively high contact angles make more claims related to long-term moisturization. Contact angles were measured according to sessile drop method using Krüss EasyDrop analysis system with attached computer running Krüss DSA1 software for device control, image acquisition and analysis of drop shape images.15 In addition, it was previously shown that water resistant properties of sunscreen products correlate with the respective water contact angles (wettability) after their application in vitro on Vitro Skin (N-19)16 and in vivo on human skin—according to Hagens et al.17
In preparing the substrate and applying the product, Vitro Skin (N-19), Lot#0231 was pre-cut and pre-hydrated as described. The application dose of the test product in all in vitro tests was 2mg/sq. cm—similar to the application density used in the in vivo tests.
Detailed description of the test products, their UVAI/UV ratios, measured contact angles and absorbance spectra after pre-irradiation are presented in the graph above and the table on p. 52.Seven test products A, B, C, D, E, F and G contain identical composition of five sunscreen actives: avobenzone, 3.0%; homosalate, 15.0%; octisalate, 5.0%; octocrylene, 10.0%; and oxybenzone, 6.0%. Products A, B, C, D and F utilize Helioplex photostabilizing patented technology3 in conjunction with maximum allowed concentration of UVB sunscreen active octocrylene to further photostabilize avobenzone. Product G employs diethylhexyl syringylidenemalonate, a photostabilizer and SPF booster6 and maximum allowed concentration of octocrylene to further stabilize avobenzone.
Products A, B, C, D, E and G are oil-in-water emulsions; all contain styrene/acrylates copolymer microspheres, an effective SPF booster that also imparts smooth skin feel,7 additional particulates and polymers that contribute to product’s efficacy and performance. Products A and B both contain plant-derived natural ingredients glycine soja (soybean) seed extract, dipotassium glycyrrhizate and chrysanthemum parthenium (feverfew) leaf/flower/stem juice. Product E contains similar ingredients as product C, but listed in different order, with additional tocopheryl acetate, butylene glycol, ascorbyl palmitate and glycine soja (soybean) protein. Product H contains only three sunscreen actives: avobenzone, 2.5%; octocrylene, 8.0%; and oxybenzone 3.5%. These concentrations are lower than those in the other seven test products; it is a water in oil system and utilizes at least two patented photostabilizing/SPF boosting technologies, AvoTriplex4 and a triplet combination of avobenzone, octocrylene and oxybenzone5 together with particulates, polymers and emollients (including UV-attenuating butyloctyl salicylate), which likely contribute to the product’s high efficacy.
Experimental data show that UVAI/UV ratios of SPF 100+ sunscreen products launched in the U.S. in 2010 are in the narrow range of 0.8-0.85; all are photostable and belong to the proposed “High UVA Protection” category (three stars) while failing to fulfill the “Highest UVA Protection” criterion (four stars). Product H has highest UVAI/UV Ratio of 0.85 and product C the lowest at 0.80.
Products A and B generated similar contact angles of about 40 degrees, suggesting that their sensory properties are similar; products C, D and E are in the range of 52-57 degrees, indicating their possible sensorial similarities as well. Products A, B, C, D and E have combinations of “light” and/or “lightweight and/or non-greasy” claims, which are consistent with correlations, established earlier.14 Product G related contact angle value of 62.9 degrees predicts its good moisturizing potential14 that is actually confirmed by moisturization claim on its label. Product H generates contact angle value of 33.9 degrees; this is the lowest value ever found among more than 50 products evaluated so far under these test conditions14,16 and may indicate good sensory properties of this product, which currently does not have any relevant claims on the package. It was previously found that the majority of lotions with “non-greasy” and/or “lightweight” claims contain a certain particulate(s) or their combination: aluminum starch octenylsuccinate, silica, etc.;14 these findings are in agreement with current data—where seven SPF 100+ products that produce relatively low water contact angles contain spherical micro particles7 and other particulates, which are simultaneously contributing to achieving SPF 100+ and beneficial sensory profiles of these products. Test product F is an alcohol containing spray that generates a contact angle of 81.1 degrees; however, this is not a prohibitive value from having “non-greasy” and “lightweight” sensorial properties claimed for this product; it may also suggest its long term moisturization potential.14 Manufacturers also describe additional skin benefits for certain SPF 100+ products: their ability to counter skin damage on cellular level, prevent deep oxidative damage, prevent the appearance of discoloration and fine lines, protect collagen and elastin from breaking down (A and B); shields skin six layers deep from skin-aging UVA rays, combats free radicals that accelerate signs of aging (C); helps shield skin from environmental damage (E); moisturizing (H).
Table: Commercially available SPF 100+ products, their UVAI/UV ratios after pre-irradiation and contact angles of water on Vitro Skin (N-19) after product application.
Comparative evaluation of eight SPF 100+ commercial products launched in the U.S. in 2010 using in vitro test methods was conducted; study demonstrated that their photostability, UVAI/UV ratios in the range of 0.80-0.85 and good sensorial attributes can be considered beneficial to the consumer. However, all these products belong to the FDA proposed “High UVA Protection” category (three stars) while failing to fulfill the “Highest UVA Protection” criterion (four stars). Reaching the highest UVAI/UV ratio (four star) for sunscreens with SPF 100+ cannot be achieved with the use of sunscreen actives currently approved in the U.S. Measurements of the contact angle of water to quantify the surface modifying effects of test products on a skin-substitute substrate suggested similarities in sensorial profiles for certain SPF 100+ products. This study helps sunscreen consumers to better differentiate SPF 100+ commercial products while providing formulators with a useful testing approach to conduct in vitro benchmarking studies and optimize development of effective sunscreen products with good sensorial profile, moisturizing and other benefits.
We are grateful for the support of Steven G. Micceri and Art Duev of Integrated Botanical Technologies, LLC, Ossining, N.Y.
1. Federal Register, 21 CFR Parts 347 and 352 Sunscreen Drug Products for Over-
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