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j. Cosmet. Sci., 49, 369-376 (November/December 1998) Reduction in the sweaty smell of 3-methyl-2-hexenoic acid by cross-adaptation using its pleasant-smelling methyl esters JOHN D. PIERCE, JR., DAVID H. BLANK, GEORGE PRETI*, and CHARLES J. WYSOCKI, Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA 19104-3308 (J.D.P., D.H.B., G.P., C.J.W.) Department of Dermatology, School of Medicine, University of Pennsylvania (G.P.) and Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania (C.J.W.). Accepted for publication October 15, 1998. Synopsis Magnitude estimates for a 10:1 mixture of (E)- and (_Z)-3-methyl-2-hexenoic acid (3M2H), a principal component of human underarm odor, decreased following adaptation to a mixture of methyl esters of 3M2H (ME3M2H), which possess a pleasant, fruity odor. These results provide further demonstration that struc- turally similar, yet perceptually distinct, odorants may cross-adapt and suggest that the extent of cross- adaptation may be affected by the degree of structural, as well as perceptual, similarity. INTRODUCTION The extent of olfactory cross-adaptation, the decrease in sensitivity to one odorant following exposure to a different odorant, may represent the degree to which odors share common sensory channels (1-4). Thus, by documenting the extent of cross-adaptation among different odorants, inferences about structure-activity relationships and coding in the olfactory system can be drawn. Yet, surprisingly little is known about the determinants of olfactory self- and cross-adaptation. The present report continues our long-term study of the structural features of odorous compounds as they affect cross- adaptation between sweaty-smelling 3-methyl-2-hexenoic acid and its fruity-smelling esters. It is now well established that the occurrence of cross-adaptation typically entails a David H. Blank's current address is Albany Molecular Research, Inc., 21 Corporate Circle, Albany, NY 12203. John D. Pierce, Jr's current address is Department of Psychology, Philadelphia College of Textiles and Science, Philadelphia PA 19144. 369