224 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table III Apparent Lanolin in Control Strippings Apparent lanolin found (ng) Male Male Male Strippings 68 years 32 years 36 years 1 to 3 36 Not measurable 11 4 to 6 15 Not measurable Not measurable Total 51 Not measurable 14 Note: results as low as these are of doubtful accuracy. DISCUSSION A sensitive method for determining lanolin in layers of human stratum corneum has been shown to give good results, taking into account interference from adhesive tape, filter paper, and naturally occurring components of the stratum corneum. The reason for choosing a ten-minute waiting period for penetration to occur before stripping was twofold. First, corneocyte shedding from the stratum corneum is a con- tinuous natural process and could be significant over a longer period, involving losses of lanolin with a resultant incomplete mass balance. The second reason is subjective, since when lanolin is used as an emollient, rapid penetration and effect is important to the user. The mass balance obtained suggests that no significant penetration of lanolin through the stratum corneum takes place, at least within the time period covered by the inves- tigation and with this particular test subject. Since about 96% of the lanolin was found in the first 40% of strippings, it seems unlikely that much, if any, penetration will occur. Whether there would be substantial inter-subject differences in penetration is not known at this stage, but it is hoped that the wider-ranging investigation as a whole may throw light on this point. As a precursor to the experiment already described in detail, a pilot trial was made which followed the same broad technique, but with some differences: 1. The lanolin was applied to the test site through the open rectangle in the template that was temporarily taped to the arm. 2. The lanolin was applied by fingertip instead of by glass rod. 3. A higher loading of 5 mg cm-2 of lanolin was applied. This was not a good method since some lanolin was forced underneath the template and thus could not be absorbed by the skin, although some was absorbed by the fingertip. Although unabsorbed lanolin was recovered from all locations by chloroform and de- termined, overall recovery was only 81.1%. Nevertheless, results were graphed and the general shape of the curve agreed closely with the one actually shown in Figure 1. Reproduction here was therefore considered unnecessary. It is also noted that the shape of the curve is remarkably similar to one obtained by King et al. (12) that related the number of corneocytes removed to the number of successive tape strippings. The majority of corneocytes were removed in the first 12 strippings. Some of the tape strippings made in the present work were examined by optical mi- croscopy before their lanolin content was determined, and the number of corneocytes

PENETRATION OF LANOLIN 225 1 m o I I I I 2 3 4 5 mg Lanolin Figure 3. Calibration curve for lanolin determination. I