ANTI-AGING EFFECTIVENESS OF RETINOL EMULSIONS 265 conductivity meter Model 101 (Orion Research Inc., Beverly, MA) were expressed in mS. ( d) Centrifugation assay. In order to verify the stability of the creams to separation, samples of both emulsions were placed in a centrifuge tube and centrifuged at 6000 rpm for 20 minutes using a 5417 centrifuge (Eppendorf, Hamburg, Germany) to check any phase separation or creaming. OPTICAL MICROSCOPE ANALYSIS This method allows one to observe the structure of emulsions and to determine the shape and size of their droplets. Both emulsions before and after storage at 40°C were analyzed using a Leitz Labovert optical microscope at 1250 magnification, equipped with a Wild MPS 46 Foto Automat Camera (Wild Leitz, Heerbrugg, CH). The microphotographs of RETI C and RETI C concentrate emulsions at opening and after ten days of storage in the incubator were reported. IN VIVO TEST In order to evaluate the anti-aging effectiveness of the two commercial products, ten volunteers, women aged between thirty-three and seventy, were submitted to trial. All the panelists were treated with the commercial RETI C and RETI C concentrate prod­ ucts supplied by Vichy, packaged in their original aluminium tubes. They exclusively employed for two months the following suitable products: a milk lotion and a tonic lotion, as cleansers, and the two emulsions, a night cream (RETI C con­ centrate emulsion) and a day cream (RETI C emulsion), as anti-aging treatments. The measures were repeated at the same hour every day and the volunteers remained at rest fifteen minutes before analysis. These measures are able to identify the microstructure of the skin surface, the wrinkles of the skin, and their evolution over time after application of RETI C and RETI C concentrate emulsions. The test was carried out employing a Microcamera Digital Plus with a monitor Flatron LCD 575 LE (LG Electronics Italia, San Donato Milanese, Italy), which allows a fifty-fold magnification of epidermis. This instrument is an advanced professional system of magnification employed to perform a checkup of the skin. The system magnifies the surface of the skin, giving a color image, and through a powerful magnification factor, allows one to individuate the examined surface particulars that are invisible to the naked eye. RESULTS AND DISCUSSION The emulsions studied were kept in the original aluminum tubes, protected from direct sunlight and sources of heat. Three months after opening, consistency, color, and smell were unmodified, and the concentration of retinol proved to be 83.8% for RETI C emulsion and 99.4% for RETI C concentrate emulsion, in comparison with the initial values found in the two products at opening.

266 JOURNAL OF COSMETIC SCIENCE RADIATION STABILITY STUDY To evaluate the stability of vitamin A, the emulsions were irradiated under UVA and UVB lamps. RETI C emulsion irradiated under UV A showed high stability during the first hour, followed by a clear decrease in vitamin A concentration. Both after 30 and 60 minutes of irradiation in the same conditions, the percentage of retinal in the cream appeared unchanged. However, after 90 minutes, the retinal concentration began slightly to decrease (5.2% of degradation). Extending the period of irradiation, the photodegradation proceeded more quickly, and the retinal degraded percentage was 27.5% after 120 minutes, 45.7% after 150 minutes, and 53.2% after 180 minutes. Figures 1 and 2 show the percentage of retinal degradation versus time under UVA and UVB irradiation for RETI C and RETI C concentrate emulsions, respectively. The photodegradation of retinal in RETI C emulsion was more progressive under UVB radiation. In fact, the percentage of degradation had already begun to increase before 30 minutes of irradiation (7 .1 % of retinal degraded percentage), and it continued to in- 60 y = 0,4897x- 32,44 R2 = 0,9641 UVA "C 50 cu "C 40 ... • •• en cu "C 30 0 y = 0,207x + 1,7536 • C: R2 = 0,9777 UVB +i 20 •UVA f . ■ .. . � 10 ■UVB 0 ••• 0 0 30 60 90 120 150 180 time (min) Figure 1. Percentage of retinal degradation in RETI C emulsion under UV A and UVB irradiation. 60 "C 50 cu "C 40 en cu 30 0 20 cu � 0 10 ....• - 0 0 30 ■ 60 y = 0, 1523x + 14,327 R2 = 0,9458 UVA . . - ... - . . • 90 time (min) y = 0, 1677x + 0,8893 R 2 = 0,9585 UVB 120 150 180 •UVA ■UVB Figure 2. Percentage of retinal degradation in RETI C concentrate emulsion under UVA and UVB irradiation.