The Great Pheromone Myth

7. Human Pheromones

SEVEN Human Pheromones Wonder not, Rufus, why none of the opposite sex wishes to place her dainty thighs beneath you, not even if you undermine her virtue with gifts of choice silk or the enticement of a pellucid gem. You are being hurt by an ugly rumour which asserts that beneath your armpits dwells a ferocious goat. This they fear, and no wonder; for it’s a right rank beast that no pretty girl will go to bed with. So either get rid of this painful affront to the nostrils or cease to wonder why the ladies flee. Gaius Valerius Catullus (87–54 BC) Whether humans have pheromones was listed by Science magazine as one of the top 100 outstanding scientific questions of 2005 (Anonymous, 2005). Over the course of the past three decades, numerous claims have been made that human pheromones influence sexual attraction, mate selection, moods, behaviors, seating patterns in of- fices, and endocrine function in both sexes. Although no chemical compounds have been isolated, in some cases specific androgen-related steroids have been assumed a priori as being human pheromones based upon their presence in human axillae and their purported pheromonal role in pigs. One group has claimed that humans possess a functional vomeronasal organ that responds to such agents in a sexually dimorphic manner (MontiBloch et al., 1994; Berliner et al., 1996). As will be shown in this chapter, evidence for the existence of human pheromones is weak on empirical, conceptual, and methodological 125 126 THE GREAT PHEROMONE MY TH grounds. While odors and fragrances, like music and lighting, can alter mood states and physiological arousal, it is debatable whether agents purported to be pheromones uniquely alter such states. The same is true for putative pheromones said to alter endocrine function, as exemplified by questionable claims of their ability to synchronize menstrual cycles, a topic considered in great detail later in this chapter. Sources of Putative Human Pheromones Humans excrete or secrete a wide range of chemicals via their urine, breath, genitalia, saliva, and specialized skin glands. Following Alex Comfort’s influential 1971 Nature paper entitled “Likelihood of Human Pheromones,” investigators have largely confined their search for pheromones to secretions from the apocrine glands within the armpits. Most seem to have agreed with Grammer et al.’s 2005 statement, “The main producers of human pheromones are the apocrine glands located in the axillae and pubic region” (p. 136). This is in spite of the fact that—as noted in previous chapters—urine and sebaceous glands are the primary sources of putative pheromones in most nonhuman mammals.1 The apocrine glands are one of three major glands that excrete materials to the surface of the human skin (Figure 7.1). Among their secretions are lipids, including cholesterol, sterol esters, triglycerides, diglycerides, fatty acids, and wax esters. Apocrine secretions are largely odorless until acted upon by aerobic diphtheroid bacteria (Leyden et al., 1981). Despite being found in some of the same body regions as sebaceous glands, emptying into the shafts of hair follicles as part of the “apo-pilo-sebaceous unit,” their highest density is within skin areas paralleling the evolutionary regression of terminal hair, such as the axillae and the perineum (Doty, 1981). These glands become functional around the time of puberty, releasing their secretions in relation to emotions associated with anxiety, fear, pain, or sexual arousal (Wilke et al., 2007). Some have suggested that their emulsifying properties serve an important thermoregulatory effect even in humans, although, in contrast to some other mammals (e.g., horses), their function is not thermoregulatory (Scott et al., 2001). Given their close functional association with anxiety and fear, it is conceivable HUMAN PHEROMONES 127 that they represent a vestigial defense system useful at one time in warding off predators or unwanted conspecifics. In contrast to the apocrine glands, the eccrine sweat glands play a significant role in regulating body temperature in humans. These three to four million glands are activated by the sympathetic nervous system during exercise and stress (Nicolaides, 1974) and are capable of secreting up Apocrine gland Hair follicle Eccrine gland Sebaceous gland FIGURE 7.1. Schematic of a pilosebaceous unit with apocrine and eccrine sweat glands. Modified from Doty (1981). 128 THE GREAT PHEROMONE MY TH to 3 l of aqueous solution per hour (Tobin, 2006). Their coiled tubules connect to the skin’s surface independently of...