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16 The Biology of Beauty Body Scent Pheromones, or the scented chemicals that are released when an individ- ual sweats, are just starting to be understood more fully in relation to human attraction and attractiveness. Pheromones are known to play a role in animal courtship, but their role in human attraction is not as well understood. The influence of pheromones takes place at an unconscious level, perhaps direct- ing one’s attention toward another individual and potentially contributing to a sense of instant chemistry with another person. But conscious decision making and interpretation of these unconscious signals definitely play a sig- nificant role in ultimate behavior and assessment. Research shows that the chemical signals we emit actually influence the hormone levels of other peo- ple. Pheromones play a communicative role in many other species, and it is likely that they have a function in human relationships as well. A woman’s scent and her sensitivity to the scent of others change over the menstrual cycle. In women, pheromones are secreted from the genital area, the area around the navel, the breasts, and the armpits. If these scents are too strong, they can create an aversive effect in the form of body odor, but, at low quanti- ties, they may be unconsciously enticing. In this way, pheromones can have a regulating effect on the hormones of those around them. A specific example is the phenomenon of the synchrony of the menstrual cycles of women who are frequently together. James Kohl from JVK Resources, Inc., along with research- ers from the University of Vienna demonstrated the effects of this hormone exposure. By exposing participants to artificial pheromones, they were able to significantly increase or decrease reported sexual attraction in participants, syn- chronize menstrual cycles, and alter mood, as compared to control groups. Body scent is also correlated with genetics, health, and immune system’s functioning. In general, a woman tends to prefer the smell of a man whose genes vary from her own. If reproduction were to occur, this variance would create diverse offspring with varied immune systems. In a genetic sense, mat- ing with a sibling would create redundancy and thus most siblings do not smell attractive to one another. In fact, they tend to smell repulsive. Women tend to be more sensitive to smells than men and, thus, may be more apt to detect and react to scents of an attractive (or unattractive) male. During ovulation, women are the most sensitive. Markus Rantala and col- leagues from the University of Jyvaskyla and the National Public Health In- stitute in Finland found that women, particularly those who were not using contraceptives, tended to rate masculine scents as more attractive while in the most fertile phase of their menstrual cycle. To examine the usefulness of smell for detection of attractiveness, Steven W. Gangestad and Randy Thornhill from the University of New Mexico asked women to smell and