222 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS transparency (whitening) of the spots, and c) increased translucency of the white tape, artificially modifying the contrast between the spots and the tape. Our objective was to establish standard conditions that would eliminate the artefacts induced by storage. We were able to prevent these by placing the Sebutape © samples on a plastic sheet rather than a black card and by storing the tapes in a freezer. MATERIALS AND METHODS Sebutape © (CuDerm Corp., Dallas, TX) was applied for one hour to the central fore- head. One sample was placed on the original black storage card (CuDerm Corp., Dallas, TX), while a corresponding one was placed on a transparent plastic report cover (C-Line products, Inc.) that we attached to the original card. Half of the samples was stored at room temperature, while the rest was put in the freezer at - 15øC. In this design, three parameters, enlargement of sebum spots, whitening of spots, and increased translucency of the tape, could be studied under four conditions of storage: a) on a plastic sheet at room temperature, b) on a plastic sheet in the freezer, c) on a black card at room temperature, and d) on a black card in the freezer. Samples were analyzed at times 0 min, 30 rain, 1, 2, 3, 5, 6, 15, and 20 hours, and 1, 2, 3, 4, 7, 14, and 30 days. Sebutape © images from a stereomicroscope (OPMI-1FC, ZEISS, Germany) were trans- ferred to an image analyzer through a black-and-white videocamera (CCD-72, DAGE- MTI, Michigan City, IN). An image analysis program was developed to scan tlae spots (analySIS, Soft-Imaging Software GmbH, Miinster, Germany). The images were pro- cessed with an edge detection filter. The sebum spots were extracted using a gray level scale. Each image was stored on a hard disc. The analysis determined the percentage area covered by sebum spots and their number and mean size. RESULTS INCREASED TRANSLUCENCY OF SEBUTAPE © No increase in translucency was observed on Sebutape © on plastic sheets either at room temperature or in the freezer. By contrast, increased translucency developed, often immediately, when the tapes were fixed on the black card. Storage in the freezer intensified this change, probably because of increased humidity between the tape and the card, while at room temperature this alteration was only minimal. Additionally, in the freezer, translucency gradually increased over time, reaching a plateau after a few days (Table I). ENLARGEMENT OF SPOTS This phenomenon correlated directly with sebum output of individual follicles. Large spots enlarged disproportionately, while small spots underwent marginal changes. At room temperature enlargement reached a peak in 5-15 hours in the freezer the spots slowly but steadily increased, reaching a maximum at seven days. After peaking, the size reached a plateau. The greatest degree of enlargement occurred in the first 30 to 60

SEBUM ANALYSIS 223 Table I Comparison of Black Card and Plastic Sheet in Freezer Density of spots/cm 2 (mean) • % Area covered (mean) 2 Storage Day 0 Day 30 Day 0 Day 30 Black card 183 205 8.37 10.5 Plastic 198 168 10.91 14.43 • Number of spots: On plastic the number of spots decreases owing to gradual fusion of neighboring spots. Increased translucency can be disregarded since it does not change on plastic. By contrast, on the black card the density of spots actually increases despite the coalescence of adjacent spots. This is because the reduction caused by fusion is more than counterbalanced by the increased translucency of the Sebutape ©, which creates spots that do not in fact represent sebum. 2 Percentage area covered: On plastic, the spots enlarge as a result of lateral seepage, increasing the area covered. On the black card, there is also an increase in area however in the latter case this is due both to seepage and to the counteracting effect of increased translucency, which allows more spots to be detected. minutes, with frequent coalescence of adjacent spots. Small spots, however, remained unchanged for the first hour, and some tiny ones disappeared (Figure 1). Enlargement of spots inevitably led to an increase in percentage area covered by sebum (Table I). At the same time the number of spots decreased, owing to coalescence of Figure 1. Enlargement of spots. Sample from an oily subject stored in the freezer. A) At time of removal. B) 20 hours later the arrows indicate identical spots that have increased in size. C) 7 days later these same spots have become even larger. This enlargement leads to fusion of nearby spots. At the same time some tiny spots disappear.