64 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS .-. 6.0 • • PRODUCT A •- PRODUCT B • 4.5 ß r 3.5 3.0 • • PRE 3 MINUTES 0.5 HOURS TIME possible to model usage situations of OTC antipruritic products. Past studies with other more invasive itch induction methods have often failed to substantiate that OTC products are effective antipruritics, even though subjective responses of con- sumers have supported the antipruritic efficacy of these products. 3. Data and results are presented that support the reliability and validity of the itch esthesiometer. The literature lacks clear validation of other methods for mild-to- moderate itch induction with respect to reliability and validity. 4. Simple perceptual ratings scales of itch depend on preexisting itch to determine the relative efficacy of products. In contrast, the itch esthesiometer produces degrees of itch based on a quantifiable stimulus. The use of the itch esthesiometer eliminates much of the variability from subjective factors such as 1) the degree of preexisting itch at a particular site, and 2) attentional and physiological changes (habituation and adaptation) to a chronic itch sensation. Further, it is often difficult to "match" preexisting itch sites within a subject, requiring the use of independent group designs (one subject, one treatment). By not experimentally controlling variability, the sample size required to detect real differences between treatments is increased, which subsequently increases study time and expense. Because the itch esthesiometer produces a discrete, isolated itch sensation, multiple treatments can be tested in the same general time frame. This "simultaneous" crossover study design, that is, using the subject as his/her own control, is a powerful method to detect true differences in antipruritic efficacy. The itch esthesiometer may be of particular value for the development of skin moistur- izers intended to relieve dry skin itch. In contrast to the invasive methods, the itch esthesiometer produces itch relevant to the recommended use conditions of many skin care products. The time course of antipruritic efficacy of these products can now be objectively evaluated. ACKNOWLEDGMENTS The authors acknowledge the contributions of Julianne Mitchell for data collection and of K. B. Hu for general guidance.

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