TRANSEPIDERMAL MOISTURE LOSS 367 Table III Results obtained for Occlusive Thickness and Per Cent Reduction of White Petrolatum Reduction (%) by Occlusive Subject Base Rate 0.1-mm Film of Thickness (mm) of Subject (mg/cm2/hr) White Petrolatum White Petrolatum A 0.39 77.5 0.38 B 0.24 90.2 0.38 C 0.32 83.0 0.40 D 0.19 93.0 0.39 Table IV Occlusive Thickness of 5•hite Petrolatums of Different Oil Contents Oil Content Occlusive Sample (%) Thickness (mm) A 52.8 2.31 B 57.O 1.35 C 61.7 0.74 D 66.1 0.39 E 70.4 0.22 F 74.6 0.13 Occlusive Thickness and Oil Content of White Petro[atum The occlusive thickness technique was applied to a comparison of white petrolatum samples of different oil content to determine if varying the oil content would give products of different occlusivity. Six white petrolatums of different mineral oil content were prepared as shown in Table IV. All of these samples meet the standards of the USP mono- graph for white petrolatum with the exception of sample A which had a consistency slightly harder than the minimum penetration specified. Four thicknesses for each sample were examined on each of three subjects. The reciprocal of the fraction reduced (l/n) was calculated and the oc- clusive thickness (S) was determined for each sample. The results are shown in Table IV and Fig. 5. The occlusive thickness decreases log- arithmically with an increase in mineral oil content. CONCLUSIONS Occlusivity, an important property of cosmetic products used on the skin, is evaluated in vivo by a new, reproducible approach which elimi- nates subject-to-subject and experiment-to-experiment variables. Char-

$68 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 4.0 3.0 2.0 !.0 S 0.6 0.4 0.2 0.! 55 60 65 70 75 OIL CONTENT (%) Figure 5. The occlusive thickness (S) of white petrolatums of different oil contents is shown as a function of the oil content in a semilog plot acterizing a product by calculating an "occlusive thickness" permits com- parison ot5 the effect o15 products on transepidermal moisture loss. (Received August 5, 1970) REFERENCES (1) Blank, I. H., Factors which influence the water content of the stratum corneum, J. Invest. Dermatol., 18, 433-40 (1952). (2) Powers, D. H., and Fox C., A Study of the effect of cosmetic ingredients, creams and lotions on the rate of moisture loss from the skin, Proc. Sci. Sect. Toilet Goods Ass., 28, 2 I-6 (1957). (3) Thiele, F. A. J., and Schutter, K., A new micro method for measuring the water balance of the human skin. Salt crystal method. I. Apparatus, J. Invest. Dermatol., $9, 95-103 (1962). (4) Thiele, F. A. J., and Schutter, K., Moisture meters for measuring the water-balance of the human skin, Proc. Sci. Sect. Toilet Goods Ass., 40, 20-4 (1963). (5) Spruit, D., and Malten, K. E., The regeneration rate of the water vapor loss of heavily damaged skin, Dermatologica, 132, 115-23 (1966). (6) Spruit, D., and Malten, K. E., Epidermal water-barrier formation after stripping of normal skin, J. Invest. Dermatol., 45, 6-14 (1965). (7) Spruit, D., Measurement of the water vapor loss from human skin by a thermal conduc- tivity cell, J. Appl. Physiol., 23, 944-7 (1967). (8) Baker, H., and Kligman, A.M., Measurement of transepidermal water loss by electrical hygrometry, Arch. Dermatol., 96, 441-52 (1967).