.l. Soc. Co.•met. ( hem. 22, 361-368 (May 27, 1971) Measurement in Vivo of Transepidermal Moisture Loss GENE R. BERIJBE, B.S., MONROE MESSINGER, B.S., and MURRAY BERDICK, Ph.D."* Presented May 26, 1970, New York City Synopsis--A technique is describcd for evaluating the effect of a cosmetic product on the rate of TRANSEPIDERMAL MOISTURE LOSS in human subjects. The thickness of product necessary to reduce the rate to zero is calculated and defined as the OCCLUSIVE THICK- NESS, a significant and inherent property of the product, independent of human subject variation. ]NTRODUCTION I,oss of water from the skin is an important physiological function. Blank (1) has stated that the water content of the stratum comeurn is probably the prime factor in determining its softness and flexibility, mak- ing the measurement of the effect of a cosmetic product on the moisture loss rate important to the cosmetic chemist. A large number of methods has been developed to measure the mois- ture loss in vivo. Noninstrumental methods such as the desiccator method of Powers and Fox (2) and the cold trapping of vapor from a stream of gas passing over the surface of the skin have been used with a limited degree of success. Thiele and Schutter (3) have described an in- strumental approach utilizing a salt crystal method. Later, these same authors presented a critical review concerning an improved salt crystal method and electrolytic methods (4). Electrolytic methods were also * Chesebrough-Pond's Inc., Research & Control Laboratories, Clinton, Conn. 06413. 361

362 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS used by Spruit and Malten (5, 6). Spruit (7) also applied a thermal con- ductivity cell to in vivo measurements. Baker and Kligman (8) used electrohygrometry to make moisture loss measurements. This paper is mainly concerned with a description of our method for isolating and measuring in vivo the transepidermal diffusion loss. EXPERIMENTAL AND R•ESULTS Description of Apparatus Figure 1 shows a general flow diagram of the apparattis which is used to measure moisture loss. Prepurified compressed air having a dew point of --59.5øC is utilized as a carrier gas. Suitable pressure reduction equip- ment is used to reduce the pressure to 5 psig. Stainless steel tubing (•/• in. o.d.) and Swagelok '©• fittings were used to connect all units. The flow of the gas was split into two streams and the flow rate in each stream was adjusted by a NUPRO ©* fine metering valve. Each stream then flows through a 4 X 4 cm Sage Instrument Probe* where the moisture is swept from the surface of the skin into the gas stream. The stream passes through the sensing chamber of a Cambridge Systems Model 990 Ther- moelectric Dew Point HygTometerõ where the amount of moisture present is measured utilizing the dew point principle. The gas exits the device through a flow meter which allows the operator to detect abnormalities in the gas flow. Crawford Fitting Co., Solon, Ohio. Nupro Co., Cleveland, Ohio. Sage Instruments, Inc., White Plains, N.Y. Cambridge Systems, Inc., Newton, Mass. INSTRUMENT , Figure 1. Schematic for apparatus used to make in vivo moisture measurements