J. Cosmet. Sci. 1 57, 261-277 Quly/August 2006) Photodegradation of retinal and anti-aging effectiveness of two commercial emulsions M. EUGENIA CARLOTTI, ELENA UGAZIO, SIMONA SAPINO, ELENA PEIRA, and MARINA GALLARATE, Dipartinzento di Scienza e Tecnologia def Farrnaco1 Universita degli Studi di Torino1 via Giuria 91 10125 Torino1 Italy. Accepted for publication April 41 2006. Synopsis Two commercial anti-aging products, RETI C and RETI C concentrate emulsions, containing retinal and vitamin C, were studied. The concentration of vitamin A was determined over time, subjecting the creams to an accelerated stability test. Both emulsions, when stored at 25 ° C, showed a moderate decrease over time in retinal concentration, while after storage at 40 ° C the percentage of retinal degraded increased over time. Under UV A irradiation, the retinal degraded to a greater extent than under UVB irradiation, both in RETI C and RETI C concentrate emulsions. In order to verify the anti-aging effectiveness of the emulsions, an in vivo test on some female volunteers was carried out, evaluating the visible results of the application of the creams on the skin surface. The creams were rather unstable after storage at 40 ° C, but they were effective in treating the signs of aging and in reducing facial wrinkles. INTRODUCTION Vitamins, like retinal and ascorbic acid, have important physiological effects on skin, all closely related to the well-known antioxidant properties of these compounds (1). Vita­ mins therefore play an important role in skin aging and may be considered interesting ingredients of cosmetic skin-care products. The formulation of finished products with ascorbic acid is impractical because this substance, readily soluble in water, is extremely unstable (2): it undergoes oxidation, especially in aerobic conditions (copper or heavy metals, in general, catalyze this reaction) and with exposure to light. These reactions occur quickly in basic conditions and the compound degrades itself irreversibly into a biologically inactive form. To overcome this problem, some authors chemically modified ascorbic acid by esterification of the hydroxyl group with long-chain organic or inor­ ganic acids. They studied the behavior of two derivatives (ascorbyl palmitate and mag­ nesium ascorbyl phosphate) in standard solutions and in cosmetic emulsions and proved that vitamin C esters are more stable than ascorbic acid (3). Moreover, in the past our Address all correspondence to M. Eugenia Carlotti. 261

262 JOURNAL OF COSMETIC SCIENCE research group has demonstrated that high protection against oxidation and degradation of ascorbic acid occurs when it is dissolved in the inner aqueous phase of the W/O/W multiple emulsion (4,5). We also demonstrated that in an W/O emulsion, ascorbic acid is more stable than in an O/W emulsion, and that the stability of ascorbic acid is increased by reducing the pH value of the inner aqueous phase (4,5). Retinoids are a large class of compounds that are important in modern therapy for the dermatological treatment of wrinkled skin (6). Retinal and its congeners are present in all living organisms, either as vitamin A or as carotenoids, some of which are provita­ mins A (7). Among the retinoids, retinal and retinyl palmitate are thought to induce thickening of the epidermis and to be effective for treatment of skin diseases (8). These functional substances, however, are known to be unstable if exposed to light or heat. A characteristic feature of retinoids is their sensitivity to ultraviolet radiation in fact, UVB and UV A radiation reduces the vitamin A content of the human epidermis (9). Although retinal and retinyl palmitate are less dangerous than retinoic acid (which, due to its irritative properties, is acceptable only for therapeutic treatment), the effect of ultraviolet rays on these compounds makes their use in dermatology more difficult. In a previous paper (10) we studied the photostability of vitamin A and of its palmitic ester in ethanol and in octyl octanoate solutions. The vitamins were irradiated alone and upon addition of sunscreens and butylated hydroxytoluene. The photostability of vita­ mins was also studied in an O/W fluid emulsion with and without butylated hydroxy­ toluene (BHT). Among the tested sunscreens, butyl methoxy dibenzoyl methane (Eu­ solex®9020) showed the strongest protective action toward vitamin A and vitamin A palmitate. Butylated hydroxytoluene inhibited the photodegradation of both vitamins, suggesting that oxygen may be involved in their degradation. In two other studies (11,12) we evaluated the protective effect of SLN (solid lipid nanoparticles) encapsula­ tion on the photodegradation and thermal degradation of retinyl palmitate introduced in different media. The aim of this work was to study the stability and effectiveness of two commercial products containing retinal in their formulations. In particular, we were interested in investigating the anti-aging effectiveness of the two products by studying the physico­ chemical stability of retinal. It is clear that the aluminum tubes and the appropriate steps adopted by the factory in packaging the RETI C and RETI C concentrate emul­ sions assure their stability during the storage period, as they minimize the contact of the functional ingredients with oxygen and light, but we were primarily interested in studying the behavior of these two products once applied to the skin. On the other hand, everybody knows that, especially during the summer season, the tubes, during storage, could be subjected to a sudden change in temperature, reaching even higher than 30°C, especially after purchase. Moreover, once applied to the skin, the thin layer of product remains there for several hours, coming in contact with lots of damaging factors like air (oxygen), UV-IR irradiation, and high temperature. In this context, our tests could be very important because they are accelerated tests of stability-hence they allow us to predict what could happen to the products in the worst conditions. MATERIALS AND METHODS Ethanol absolute and methyl alcohol were purchased from Carlo Erba, aluminum sulfate was from Schiapparelli, octyl octanoate was a gift from Dragoco, and all-trans-retinal