]. Cosmet. Sci.} 55, 139-148 (March/April 2004) Photostability of naturally occurring whitening agents in cosmetic microemulsions M. GALLARATE, M. E. CARLOTTI, M. TROTTA, A. E. GRANDE, and C. TALARICO, Dipartimento di Scienza e Tecnologia def Farmaco, Universita di Torino, Via Pietro Giuria, 9 10125 Turin (M.G., M.E.C., M.T., A.E.G.), and Perlarom, Turin (C. T.), Italy. Accepted for publication July 29, 2003. Synopsis An o/w microemulsion formulated using lecithin and an alkyl glucoside as mild, non-irritant surfactants was proposed as a cosmetic vehicle for arbutin and kojic acid, naturally occurring whitening agents. After assessing the physicochemical stability of the microemulsion in the presence and absence of whitening agents, several perfumed compositions, developed using fragrant molecules of natural or synthetic origin, were introduced, and the olfactory impact of the perfumed microemulsion was evaluated. The photostability to UVB irradiation of both whitening agents was determined in aqueous solutions and in microemulsions, and also in the presence of the perfumed compositions. The stability of arbutin and kojic acid was higher in microemulsions than in aqueous solutions, and only in some cases did the presence of odorous molecules appear to influence it: linalool exerted some protective effect towards kojic acid photo­ degradation. INTRODUCTION Melanin is an important defense of human skin against the harmful effects of UV light pigmentation also has an important cosmetic significance that can be altered in some hyperpigmentation disorders, such as melasma, spots, and postinflammatory hyperpig­ mentation (1). Skin-whitening products are very popular and are used to lighten the skin and to treat freckles and skin hyperpigmentation such as senile lentigines their effec­ tiveness depends on the choice of an appropriate whitening or depigmenting ingredient (2). There are two principal ways of lightening the skin by reducing pigmentation: discoloring the melanin already present in the upper layers of the epidermis and/or preventing new melanin from being formed. One of the most suitable substances for use in skin bleaching products is hydroquinone, whose mechanism of action is related to its ability to inhibit the enzymatic oxidation of tyrosine to 3,4-dihydroxy phenylalanine (3). Address all correspondence to M. Gallarate. 139

140 JOURNAL OF COSMETIC SCIENCE Italian law has recently prohibited the use of hydroquinone in cosmetics (4), owing to its skin-irritant effect and to its potential involvement in carcinogenesis, so that most formulators are now interested in the use of naturally occurring whitening agents such as kojic acid and arbutin. Kojic acid, produced by many species of Aspergillus and Penicillum in an aerobic process (5 ), possesses an excellent whitening effect, owing to tyrosinase inhibition activity that is probably due to a copper chelating action. It can also prevent serious sunburn caused by an accumulation of melanin in subcutaneous tissue produced via a tyrosinase­ catal yzed metabolic pathway (6). Arbutin is an active ingredient found in plants such as bearberry (Arctostaphylos uva-ursi), and has long been used in Japan as a chemotherapeutic agent against a number of pigmentary disorders (7). Although its action mechanism is probably similar to that of hydroquinone, it is much less cytotoxic to melanocytes in culture (8). Unfortunately, both arbutin and kojic acid may undergo photo-and/or thermodegradation in aqueous solution (9), involving modifications in their chemical structure, loss of organoleptic properties, and darkening of formulations, making it difficult to obtain stable and effective products. In this experimental study, with the aim of enhancing the UVB photostability of both whitening agents, cosmetic microemulsions obtained with mild, naturally derived sur­ factants (10) were formulated and characterized. Some perfume formulations, developed and characterized in our research laboratory (11) using fragrant molecules belonging to different chemical groups, were also introduced in the microemulsions to evaluate the olfactory impact of the perfumed microemulsion and the effect of the fragrances on its stability in the presence and absence of whitening agents. The influence of perfumed compositions on the photostability of arbutin and kojic acid in microemulsions was also investigated. EXPERIMENT AL METHODS MATERIALS Microemulsions. Arbutin, kojic acid, 1,2-hexanediol, isopropylpalmitate [IPP], and 2-methyl-2,4 pentanediol (hexylene glycol) were from Aldrich sodium hydroxide and methanol were from Carlo Erba tetra hexyl ammonium chloride was from Sigma absolute ethanol and hydrochloric acid were from Fluka soya phosphatidylcholine 96% (lecithin) {SPC] Epikuron®200 was from Lucas-Meyer decyl polyglucose Oramix®NSIO (decyl polyglucose), a.s. 0.55%, was a gift from Seppic. Fragrances • Coconut: Ethanol 68.5% water 29.6% -y-octalactone 1 % -y-butyrolactone 0.5% vanillin 0.4%. • Fragrance: Ethanol 55.8% hydroxycitronellal 14.26% tetrahydro linalool 14.26% oak musk abs. 9.0% tibetolide 3.56% Turkish rose e.o. 1.8% a-hexyl cinnamic aldehyde 1.24%. • Orange: Orange 1/10 e.o. 45.0% sweet orange e.o. 45.0% orange terpenes 4.4% ethyl butyrate 1.5% aldehyde CS 1.04% orange heart 0.731 % isoamyl butyrate 0.55% lauryl alcohol 0.475% a-ionone 0.379% acetaldehyde 0.27% linalool