JOURNAL OF COSMETIC SCIENCE 200 factor (SPF) is still considered by many consumers and some physicians as the main crite- rion to choose a sunscreen. In addition to UVB protection, not only the protection against long-wave UVA (and in some conditions against visible light and short infrared) but also the stability of the fi lters, the esthetic of the formula, and practicability and ability of the fi nal product to homogeneously cover the entire skin are key factors that must be taken into consideration for an optimal formulation of a sunscreen. DEVELOP MENT OF MORE EFFICIENT SUNSCREENS CHOOSIN G THE APPROPRIATE FILTERS The rec ognition of UV-induced skin damage prompted the development of products of- fering greater protection against UVB and UVA radiation. Well-balanced protection against UVB and UVA radiation was defi ned in the 2006 EC recommendation (15) as an SPF-to-UVA protection factor (UVAPF) ratio of d3 (e.g., UVAPF at least 20 for SPF50+). This requirement has therefore been adopted in other countries worldwide. The UVAPF is determined according to International Organization for Standardization (ISO) (16,17) using the persistent pigment darkening (PPD) endpoint representative of UVA damage. Increased UV protection requires higher concentrations of UV absorbers, but their un- pleasant, greasy feeling may induce low cosmetic acceptance. Therefore, formulators must create elegant yet effective sunscreens with less UV fi lters but the same level of UVB/ UVA protection. Balanced protection requires a combination of lipophilic and hydro- philic absorbers in the UVB, short UVA, and long UVA (18). An examp le of synergy of organic UV fi lters is offered by mixing terephthalylidene dic- amphor sulfonic acid (Mexoryl® SX, Noveal, Le Thillay, France), a “short UVA” fi lter, with drometrizole trisiloxane (Mexoryl® XL, Noveal) and bis ethylhexyloxyphenol me- thoxyphenyl triazine (Tinosorb® S, BASF, Ludvigshafen, Germany), two broad UVB/ UVA fi lters. All three are photostable and are part of Mexoplex® technology (18). An- other example is offered by nanosized titanium dioxide (an inorganic UV fi lter) that, combined with organic UV fi lters, produces a high SPF through synergetic effects. Formulations should be photostable and not be degraded during exposure to sunlight (19). Formulators should ensure persistence of protection during exposure by using a photostable fi ltering system. The UV fi lte r avobenzone (butylmethoxydibenzoylmethane or BMDBM) has a very high molar extinction coeffi cient in the UVA1 wavelengths, but it is degraded signifi cantly on exposure to UV (20). This photo-instability is enhanced by the UVB fi lter ethylhexyl methoxycinnamate (21), so this combination should be avoided. Potent avobenzone photo- stabilizers include octocrylene, a UVB fi lter, Tinosorb® S (22–24), and the biodegradable oil Eldew® SL-205 (Ajinomoto, Tokyo, Japan), a sarcosine derivative, are used in the Mexoplex® technology (18). IMPORTANCE OF M AXIMIZING EFFICIENCY AND COMPLIANCE Increasing effi cacy while improving consumer observance irrespective of age and skin types requires products with good spreadability, pleasant feel, and transparency on the skin. Homogeneous distribution of UV fi lters is essential for maximizing effi cacy.
SUNSCREENS FOR OPTIMAL PROTECTION EFFICACY 201 FORMULATION DES IGNED FOR EFFICACY Sunscreens are generally made of oil-in-water emulsions, with the fi lter dissolved in oil droplets dispersed in a water phase. When applied, the droplets spread over the skin sur- face to form an organized network of UV fi lters: the more evenly the emulsion spreads, the higher is the performance of the fi lter. New Netloc k technologyTM is based on a semicrystalline polymer (INCI C12-22 alkyl acrylate/hydroxyethylacrylate copolymer, L’Oréal, Clichy, France) that gels and stabilizes the oil droplets without the use of surfactants. The resulting emulsion consists of gel microdroplets that lock in the UV absorbers. After application, these gel droplets create an optimal fi lm on the skin with constant thickness, even coverage, and a fi ne, homoge- neous distribution of UV fi lters. This fi lm anchors and adheres to the microreliefs of the skin, conveying high effi cacy and resistance to stresses such as water, sweating, and sand. The SPF-enhanci ng properties of this technology is illustrated by the comparison of three oil-in-water emulsions containing the same association of UV fi lters (at the same concen- tration), with an expected SPF of around 50. The SPF was measured in vivo following ISO 24444–2010. The formulation based on the Netlock technologyTM yielded an SPF twice as high as the other formulations based on classical emulsifi ers (Figure 1). The resistance to stress afforded by this technology was evaluated by applying sunscreens on volunteers who then conducted normal daily activities, such as offi ce work (3 h), lunch, and workout on a treadmill (20 min), followed by the application of a water mist. The UV absorption capacity of the sunscreens was evaluated by pictures taken under UV light: the absorption capacity of the classical sunscreen reduced signifi cantly but remained unchanged for the sunscreen based on the Netlock technologyTM (Figure 2). Figure 1. SPF values of three sunscreens containing the same UV fi lters ass ociation (expected SPF 50): The sun- screen based on Netlock technologyTM obtained a SPF value twice as high as the other two sunscreen products.
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