J. Cosmet. Sci., 69, 131–143 (March/April 2018) 131 Reducing Facial Wrinkle Size and Increasing Skin Firmness Using Skin Care Polymers MARC N.G. DE MUL, TANYA UDDIN, XI YAN, AMBER HUBSCHMITT, BJÖRN KLOTZ, and WENDY KIN MAN CHAN, BASF Corporation, Tarrytown, New York, NY 10591 (M.N.G.d.M., T.U., X.Y., A.H., W.K.M.C.) and BASF Personal Care and Nutrition GmbH, Düsseldorf 40589, Germany (B.K.) Accepted for publication January 28, 2018. Synopsis Many cosmetic polymers shrink on drying, producing a tensile force if coated on a substrate. This tensile force can be used to smoothen wrinkles and pores in facial skin. In this study, we evaluated two polymers, a polyvinylpyrrolidone (PVP) and a polyacrylate, for skin tightening properties. We conducted a double-blinded, placebo-controlled and randomized clinical study with 32 female volunteers aged 35–65 years who perceived themselves to have a loss of skin elasticity. Both polymers were formulated in a model cosmetic emulsion with hydrogenated polyisobutene as the oil phase. We measured skin fi rmness and tightening parameters at baseline and after each product application. Also, facial images were recorded with a fringe projection instrument. The fi rming measurements indicated that both polymers instantly tightened facial skin, whereas the placebo product offered no signifi cant tightening benefi t. However, in clinical evaluation, only the polyacrylate polymer produced statistically signifi cant improvements in wrinkle size and skin fi rmness on the face without signifi cant consumer use complaints such as tackiness. We concluded that skin care products using PVP and polyacrylates have the potential to offer immediate and visible benefi ts to consumers with aged skin. INTRODUCTION Erasing the effects of age on the face is one of the most elusive benefi ts that consumers seek in skin care products. Myriad products are available in commerce today that claim to make consumers appear younger. However, most work by fi lling in and covering up wrinkles, age spots, and other attributes of aged skin, and others have effects on aged skin that are measured as relatively small improvements over prolonged treatment periods. All must be applied daily for a sustained effect, in contrast to surgical treatments that have a long-term benefi t. Antiaging skin care products generally contain emollient oils and emulsifi ers in an aqueous base. Such products moisturize the skin and may improve the tactile properties perceived Address all correspondence to Marc N.G. de Mul at marc.demul@basf.com. This work was funded by BASF Corporation.

JOURNAL OF COSMETIC SCIENCE 132 by users. Active ingredients can be included to achieve other benefi ts, such as skin plump- ing that smoothes out wrinkles and biological effects on the skin microstructure and me- chanical integrity. However, biological product claims in cosmetic products are generally limited by regulatory authorities, because the long-term physiological effects of the ac- tive ingredients may not be known. Other antiaging ingredients in skin care products provide an optical effect to hide wrinkles and pores by covering up such imperfections with pigments and fi lm formers. In contrast, products that achieve antiaging effects such as wrinkle and pore size reduction by mechanical means, rather than optical or biological, have not received much attention in the literature. In addition to active ingredients, skin care products may also contain polymers mainly for their properties as thickeners, rheology modifi ers, and fi lm formers. The process of coat- ing, spreading, and drying of cosmetic emulsions containing polymers is not well under- stood (1). The mechanics of emulsion application, phase behavior of the multicomponent emulsion formulation, polymer deposition and crystallization, skin formation, and surface tension–driven fl ows (Marangoni fl ows) all play a role. The drying process of cosmetic emulsions with polymers may not result in homogeneous fi lms (2,3). In contrast to the drying behavior of aqueous polymer solutions, drying phenomena in polymer dispersions (latexes) have been extensively studied (4–6). The fi lm formation process in those systems is made up of three steps: evaporative drying and ordering of the polymer particles, particle deformation, and polymer diffusion followed by merging of the particles. Signifi cant internal stresses can build up in the polymer fi lm during drying. These can be large enough to cause coating defects or deform the underlying substrate by the shrinking of the fi lm (7). Shrinkage of the fi lm starts at a certain volume fraction of solvent in the fi lm, which is correlated with the glass transition temperature of the polymer Tg, which itself depends on the solvent volume fraction (8). When the glass transition is reached, the polymer chains become less mobile and are unable to fl ow in response to the drying stress, which causes fi lm shrinkage. Polymer fi lm shrinkage has been used to obtain a visible reduction in the size of fi ne lines and wrinkles. Various polymers produce this effect, including bovine serum albumin (9) and synthetic hair styling polymers (10). These materials have a Tg near ambient condi- tions. Skin covered with a thin fi lm consisting of these polymers experiences tightening when the fi lm shrinks on drying and contracts mechanically. In addition to the tightened skin feel experienced by test subjects, the mechanical properties of the skin are measur- ably changed (11). This polymer fi lm shrinkage is a different phenomenon than the stratum corneum shrink- age that is observed when skin is stripped of its surface lipids by surfactant solutions. In that case, consumer-perceivable tightening is caused by dehydration of the underlying skin layers (12,13). In this work, we studied two fi lm-forming polymers with relatively high Tg values, a poly (vinylpyrrolidone) (PVP) polymer and an acrylate/methacrylamide copolymer (AMC) (14). For PVP, the Tg decreases as the weight fraction of water in the polymer solution increases, reaching room temperature at 75–90 weight percent PVP, depending on the molecular weight of the polymer (15). Following the model described previously, fi lm shrinkage and skin tightening is expected when the fi lm has lost enough water through absorption and drying to reach such high polymer levels. The AMC polymer was chosen because its Tg value is the highest in a portfolio of commercial hair styling polymers.