C :.;:::. 90 L... m Z"' "'C C Cl) Cl) 0 m L... L... Cl) e a. 70 Cl) - C 0 60 C 50 100 "'C 90 ·u nJ -� 80 "a'.-. � ... C "'C a a 0 70 "'C I... nJ a a. C)._, 60 a "'C 50 C 40 0 0 PHOTOSTABILITY OF WHITENING AGENTS 145 1 2 3 4 5 6 time (hours) Figure 1. Photodegradation of 0.25% w/w arbutin. 1 2 3 4 5 6 time (hours) Figure 2. Photodegradation of 0.25% w/w kojic acid. -+-aqueous sol. ......,._sol.a --+-m.e. -e-m.e. citral ---m.e. linalool � aqueous sol. ___..,._sol.a -+-m.e. �m.e. citral �m.e. linalool overcome this problem. Since many odorous molecules are photounstable ( 15, 16) and can also negatively influence the photostability of cosmetic ingredients, the influence of these perfumed compositions on the stability of kojic acid and arbutin in the micro­ emulsion was investigated.

146 JOURNAL OF COSMETIC SCIENCE The addition of perfumes to the microemulsions did not significantly influence the photostability of arbutin (Figure 3). The whitening agent was protected against pho­ todamage in the microemulsion, even in the presence of the various odorous molecules. A similar trend was observed for kojic acid: all perfumed compositions studied appeared to offer some protection to kojic acid (Figure 4). This was particularly significant for orange and violet, the latter having the surprising result of 85% non-degraded kojic acid after five-hour-DVB irradiation. These results can probably be ascribed to the presence of linalool in both perfumes: as seen in previous experimental work (10), linalool appears to exert some protection against autoxidation in microemulsions, thanks to the good stability of its tertiary allylic free radical, which has the potential to terminate many oxidative chain reactions. To verify this hypothesis and to evaluate the influence of model odorous molecules on the photostability of both whitening agents, citral and linalool were also separately added to the microemulsion. Linalool appeared not to influence the photostability of arbutin, while citral determined a certain decrease in stability, comparable to that occurring in aqueous solutions moreover, the photostabil­ ity of kojic acid was improved by the presence of linalool (Figures 1 and 2). As citral and vanillin, whose oxidative instability is well known (15,16), were present among the several other odorous molecules in the perfume compositions, some photo­ degradation experiments were also performed evaluating the disappearance of these two molecules after UVB irradiation they were added to the microemulsion with no whit­ ening agent or with kojic acid, to verify whether the presence of the whitening agent or kojic acid could influence the photostability of citral and vanillin. 100 C 95 .c 90 L... ca "'C C a, a, "'C � 85 � a, C) a. a, - 80 "'C C a C 75 70 0 1 2 3 4 time (hours) 5 --f- m.e. -.......orange --+-coconut --violet �tea ---1::r-fragrance 6 Figure 3. Photodegradation of 0.25% w/w arbutin in perfumed microemulsions.