There has been relatively little research done on the study of human pheromones, and science has not yet discovered how these biochemical signals elicit responses in other humans. Scientists do know that pheromones are species-specific chemical messages that cause others to exhibit unlearned behaviors and physiological responses (Karlson & Lusher, 1959; Berscheid & Regan, 2005).
There is some evidence to suggest that pheromones play a role in human behavior on a regular basis. For example, research has shown that in many nonhuman mammals, pheromones guide sexual behavior (Azar, 1998; Cohn, 1994). The chemicals androstenol and androstenone are pheromones that influence the behavior of pigs, and are also found in the urine and sweat of human males, and to a lesser extent, females (Gower & Ruperelia, 1993). If these biochemical signals have an effect on pigs, they may also affect human behavioral responses.
Another piece of evidence is the fact that humans are able to recognize other people on the basis of smell from the time they are born (Cernoch & Porter, 1985). Finally, research suggests that humans have a nonvestigial vomeronasal organ in their nasal cavaties, which is a structure that contains pheromone receptors in nonhuman animal species (Garcia-Velasco & Mondragon, 1991). Human's nonvestigial vomeronasal organs may have become unnecessary with the invention of written and verbal communication, which may have caused the organ to lose much of its function through human evolution.
Other research that supports the existence of human pheromones has shown that both men and women have apocrine glands that produce odors in their armpits, nipples, and genital areas, which start to become active during puberty and may influence reproduction (Cohn, 1994). For example, heterosexual women who have sexual intercourse experience more regular menstrual cycles than women who do not have sex very often, which researchers have postulated could be due to the exposure of male apocrine gland secretions (Cutler, Preti, Huggins, Erikson, & Garcia, 1985).
Additionally, women who are exposed to the perspiration of other women experience an increase or decrease in the length of their menstrual cycles. This has the effect of causing their menstruation to sync up, depending on where the women are in their cycles: before or after ovulation. The experimenters speculate that there may be two types of pheromones involved. One pheromone produced prior to ovulation may shorten the menstrual cycle and one produced after ovulation may lengthen the cycle (McClintock, 1971; Stern & McClintock, 1998). The studies mentioned examined the effects of pheromones on sexual responses in humans but no research has been done on the influence of pheromones and how they may signal stress responses in other individuals.
The present study's goal was to investigate how high levels of stress in one member of a married couple may influence stress levels in the other partner through chemical signals alone. The study also addressed whether the length of the relationship had any effect on the incidence of stress responses.
The present study sought to determine if married couples are influenced by each other's stress levels through pheromones and whether the length of the marriage predicts the level of influence of those pheromones.
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