3-Hydroxy-3-methylhexanoic acid (1) and the 3-sulfanylalkan-1-ols 2 ± 5 were identified to contribute to the odor of human axillary sweat. Quantitative analyses of axillary sweat extracts from 50 healthy men showed an unambiguous correlation between the detected levels of 1 and the intensity of the axillary odor. Chiral-GC analyses revealed 1 to be a 72 : 28 mixture of the (S)/(R)-isomers. Optically pure (S)-1 (> 97% ee) emanated a strong spicy note, which recalled typical axillary odors. 3-Methyl-3-sulfanylhexan-1-ol (2), the enantiomeric ratio of which equaled that of 1, was present in greater quantity than any of the other 3-sulfanylalkanols. Optically pure (S)-2 (> 97% ee) had a strong meaty, fruity note, also reminiscent of axillary odor. The compounds identified, in particular (S)-1 and (S)-2, contribute significantly to the olfactory impression of human axillary odor.Introduction. ± The human body generates a variety of different odors. Scalp, hair, mouth, axillae, foot, and even the general skin surface all possess characteristic odors that are formed by septic action due to bacterial degradation. Of all the human scents, axillary odor is probably the most powerful and impressive. The axillary odor has been examined and discussed from an analytical, biological, and behavioral-physiology point of view. In particular, there is a wealth of information suggesting that it may contain chemical signals that affect the menstrual cycle [1] or may be involved in mate selection depending on a major-histocompatibility-complex (MHC) allele [2]. There are also several reports on actual axillary odorants [3], of which (E)-3-methylhex-2-enoic acid (3M2 H; see below) is considered one of the most important. 3M2 H was first reported by Zen and co-workers in 1991 [3d], who analyzed axillary odors collected from Americans, and, since then, researchers have mainly focused on this unsaturated acid. However, our own experiments have established that 3M2 H is not solely responsible for axillary odors. After a thorough analysis of the chemical composition of axillary odor, we discovered two new constituents, which also contribute significantly to the overall odor. One of them possesses a spicy note, while the other has a sulfury odor.Results and Discussion. ± 1. Analysis of the Spicy Constituent. A total of 50 healthy Japanese male volunteers were asked to collect their underarm odors by wearing clean white T-shirts that had fully defatted cotton inserts stitched into both of the armpit positions. Each insert was evaluated: 20% of the volunteers showed typical axillary odors, and 80% had a sour, acidic odor. The inserts were extracted with diethyl ether, and the ethereal extracts were treated with base. As this made the strong distinctive spicy odor disappear, the characteristic axillary odor was apparently caused by acidic