Facts, fallacies, fears, and frustrations with human pheromones.

Among primates in general, pheromones are of variable importance to social communication. Data on humans have generated the greatest controversy regarding the existence of pheromonal communication. In this review, the likelihood of pheromonal communication in humans is assessed with a discussion of chemical compounds produced by the axilla that may function as pheromones; the likelihood that the vomeronasal organ (VNO), a putative pheromone receptor organ in many other mammals, is functional in humans; and the possible ways pheromones operate in humans. In the human axilla, the interactions between the cutaneous microflora and axillary secretions render this region analogous to scent glands found in other primates. Both the chemistry of axillary secretions and their effects on conspecifics in humans appear to be analogous to other mammalian pheromone systems. Whichever chemical compounds serve a pheromonal function in humans, another unknown is the receptor. Although the VNO has been implicated in the reception of pheromones in many vertebrates, it is not the only pathway through which such information has access to the central nervous system; there is ample evidence to support the view that the olfactory epithelium can respond to pheromones. Furthermore, if a chemical activates receptors within the VNO, this does not necessarily mean that the compound is a pheromone. An important caveat for humans is that critical components typically found within the functioning VNO of other, nonprimate, mammals are lacking, suggesting that the human VNO does not function in the way that has been described for other mammals. In a broader perspective, pheromones can be classified as primers, signalers, modulators, and releasers. There is good evidence to support the presence of the former three in humans. Examples include affects on the menstrual cycle (primer effects); olfactory recognition of newborn by its mother (signaler); individuals may exude different odors based on mood (suggestive of modulator effects). However, there is no good evidence for releaser effects in adult humans. It is emphasized that no bioassay-guided study has led to the isolation of true human pheromones, a step that will elucidate specific functions to human chemical signals. (c) 2004 Wiley-Liss, Inc.