Biology 202
1999 Final Web Reports
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Following Your Nose to Optimal Sexual and Reproductive Health and Happiness

Debbie Plotnick

Like most wives, sometimes I drive my husband crazy. And even though he's a good sport about it, one of the most consistent ways in which I do so relates to one of my most pronounced idiosyncratic behaviors. For example, we will arrive appropriately early on a Saturday night at a theater to see a movie that will undoubtedly be sold out. And after picking the perfect seats, (one for him that gives him room to stretch out his long legs, and one that affords me the ability to have room to see around anyone who sits in from of me who will inevitably be much taller than I) and then I'll get up and move. What, you may be wondering, would cause me to behave this badly?

Well, it is really a matter self-protection. It's because of all the people who have been socially conditioned to interfere with nature and act upon the belief that they must be disinfected, deodorized and then re-fragranced. While this may be a headache for my husband, for me it could be a migraine. Many migraine sufferers report that strong smells can trigger a migraine (1); and in my case, perfumes are among the worst offenders.

Of course, people are not setting out to make life uncomfortable for those, like me, with hypersensitivities to chemical odors. But discomfort or even extreme pain is often the consequence of people's over utilization of substances that remove their natural fragrances and their replacement of them with chemical substitutes. However, it is my contention that it may also be detrimental to the health and happiness of those who engage in such practices.

Americans, in particular, have been taught that human body odors and secretions are offensive. And consequently they wage a daily battle against those that their own bodies produce and hope that others will do the same. However, those dreaded smells and secretions play an important role in many human behaviors, most notably those related to sexuality and reproduction and the health of those systems.

But some of the time, much to my husband's relief, I actually can tolerate the chemically scented world in which we live better than at other times. The intensity of my sensitivities wax and wane in accordance with my menstrual cycle. This is because a woman's ability to smell varies over the course of her cycle and at the time of ovulation is believed to increase over 1,000 fold from that of the time of menstruation (2). It is the fluctuations of the predominant female sex hormone estrogen that is responsible for this change in olfactory ability. And conversely women's sense of smell diminishes after menopause. It becomes particularly deficient in the ability to detect musk odors, which are produced by the predominant male sex hormone testosterone (2). Which leads me to conclude that women at the time of ovulation are sniffing around for men.

Hormones, as do neurotransmitters, influence behaviors within the nervous system and cause behaviors to occur that are observable outside of the nervous system. Hormones and neurotransmitters are similar in that both types of neurosecretory cells have specific target cells and they only effect the physiology of cells that have these receptors. However, unlike neurotransmitters which target only neurons, hormones travel through the blood to many types of target cells. Hormones are produced within the pituitary, which is located in the brain below the hypothalamus and information for release is obtained from the hypothalamus., When hormones are released into the blood effect a wide variety of cell types. "For example, estrogens, the female sex hormones, can bind to special estrogen receptor sites in uterine, heart, breast and bone cells" (3).

The menstrual cycle is controlled by both positive and negative feed back loops. The cycle begins with the first day of a woman's period. This first part of the cycle is where the endometrium, (the build up of the lining of the uterus), is expelled from the body along with a little blood. The volume of material shed ranges from a quarter to a half-cup. This phase is followed by the follicular or proliferative phase where a positive feed back loop is created as the body produces a hormone called follicle-stimulating hormone (FSH). "Follicle-stimulating hormone promotes the growth of a follicle (egg sac) within the ovary where an ovum matures in the follicle. FSH also stimulates the ovary to produce increasing amounts of estrogen. In turn, the estrogen causes endometrial tissue to build up (or proliferate), lining the interior of the uterus" (4). Around day fourteen of the cycle ovulation occurs as a mature ovum is released to travel down the fallopian tube to the uterus. And then begins the negative feed back portion of the cycle as "estrogen and progesterone exert a negative feedback influence on LH and FSH release" (5). This negative feed back continues through the last phase of the cycle know as the luteal or secretory phase. After the release of an ovum the follicle from which it was released becomes a sac known as the corpus luteum. It produces a hormone called luteinizing hormone (LH) which causes the corpus luteum to grow and to secrete progesterone, another female hormone. Progesterone makes the endometrial lining thicken in preparation for implantation of an embryo if fertilization occurs. If fertilization has not occurred then progesterone will peak about a week after ovulation and then both progesterone and estrogen production will decline and the corpus luteum will wither. This exerts negative feed back until menstruation begins and a positive feed back loop again is established.

But sex hormones are not the only chemical messengers that make loops within the nervous system. And some of the other types of messengers create loops not only within the body of the individual from which they originated but they cause changes in the nervous systems of other individuals that are in close proximity. A stimulus from outside the nervous system going in and effecting a change within the nervous system is referred to as affererence. And efference is the term for something inside the nervous system that causes a change that is projected outside of the nervous system. Afference and efference flow back and forth forming "reafferrent loops." Some of the most interesting loops occur between the nervous system of women and those of men.

My husband is a charming fellow, most solicitous and of course I am flattered by his attention. But I chuckle to myself when he calls me a "siren," thus alluding to one of the other ways in which women can drive men crazy. As much as I'd like to believe his flattery applies only to my special charms I know that not to be true. All women emit a siren song and the intensity of their call increases along an evolutionarily prudent scale. And around the time of ovulation not only is my sense of smell increased but additionally I (as do all women) generate more potent scents. Therefore, in spite of my aforementioned exasperating behaviors, that peak at mid-menstrual cycle, so does my husband's amorous behavior and exclamations as to my allure. For years I have known that he knows when I ovulate. But he doesn't know that I know. This is because his "I" function is not aware of the fact that he possesses such information.

Recent research has confirmed my observation. Men do respond physiologically to women when they ovulate. Astrid Jutte at the Ludwig Boltzmann Institute for Urban Ethology in Vienna confirmed the physiological changes with the following experiment. "Three groups of men were asked to inhale one of three synthetically produced human copulins-fatty acids found in vaginal secretions in women at various times during the menstrual cycle. One of the copulins mimicked ovulation, one menstruation and the third another point in the cycle. The fourth group of men inhaled only water vapor. Jutte found that testosterone levels in the saliva of those men exposed to the scent of ovulation increased by half, while levels in those sniffing only water dropped by half" (6). And of course, these physiological changes often influence men's behavior.

However, one of the reasons why these unrecognized influences bypasses men's "I" function is that an important component of women's fragrance is believed to be determined by pheromones. The word pheromone comes from the Greek "pherin" (to carry or transfer) and "hormone" (to excite) (7). Pheromones themselves are believed to be odorless component of humans' scent and are consciously undetectable to the human nose. Most chemical components that make up human odors are detected by the main olfactory epithelium (MOE), located deep within the nose. Most olfactory sensory messages go directly from the olfactory epithelium to the cerebral cortex, the part of the brain associated with higher order thinking and conscious behaviors. However, it is believed that pheromones are detected in humans by a tiny group of cells in the nose called the vomeronasal organ (VNO) (8). The VNO has separate neural pathways from those of the MOE. The neural projections of the VNO go to the amygdala and hypothalamus, areas of the brain associated with more primitive behaviors and emotions and controls hormone release via the endocrine system. (9). And even though pheromones may be diluted and the perception of them clouded by perfumes and other remnants of society's obsession not to allow humans to smell human, they are not totally obscured. And amazingly, in spite of the enormous efforts that are made to inhibit their transport mechanism they are still powerful enough to deliver the intended messages. Of course, every person's scent and pheromones are unique displaying intrinsic variability that is influnced by the individual's gender, heredity, diet, health, medications and mood.

Pheromones are transported from inside the body to outside the body through sweat. They are produced within the apicrine glands, one of the body's two types of sweat glands. The eccrine sweat glands secretes saline, that affords perspiration its characteristic saltiness, and the two types of secretions mix together The pheromone producing apocrine glands are located in places on humans that are "furry," such as armpits, face, nipples and genital regions. Of course the degree of furriness varies according to gender, however, again in contrast to nature's intentions, the prevailing social customs often render these body areas "unfurry." But one of intended functions of body hair helps is the promotion of pheromones and other identifying and engendering scents. Regardless of current social practices this makes sense from a practical point of view. And can be a definite advantage as noted in A Natural History of the Senses by author Diane Ackerman who wrote: "Because females have often been responsible for initiating mating, smell has been their weapon, lure and clue" (2).

Of course these chemical messages are produced by both genders and are species specific. And pheromones generate a physiological and/or behavioral response in both sexes. "Most definitions also include the requirement that this chemical communication be mutually beneficial" (10). Pheromones are composed of carbon compounds that form volatile organic acids. And they are dispersed in either gasses or liquid and are usually received by either olfactory (smell) or gustatory (taste) means. The liquid in which human pheromones is contained (sweat) is produced in body areas that are quite warm, thus precipitating their release into the air because of the pheromones' volatility at relatively low temperatures. Women's pheromones waft and can be detected at some distance. However, it is believed that men's can only be perceived at close proximity (2). Once received, pheromones have two types of effects. There is the releaser effect that precipitates an immediate change in the behavior of the recipient. And there is the primer effect, which initiates a chain of physiological events (10).

But more than just "The Harvard Law of Animal Behavior," the "I" function or sexual preference appear to be determinates for a reciprocal sexual response due to the detection of human pheromones. Some pheromones produce a very strong and immediate effects while others engender very little. Research conducted at the University of Bern in Switzerland by zoologist Claus Wedekind showed that Major Histocompatibility Complex (HLC) plays an important role determining the response to human pheromones. HLC is one of the "recognition proteins" of the immune system. It is present in most cells and is unique to each individual; however, it is very similar in siblings and is closely related among other biological family members. Dr. Wedekind's experiment involved tee shirts worn by 44 men for two days. The tee shirts were then smelled by 49 women who showed a decided preference for the shirts of men who's HLC was markedly different from their own (10). This leads me to conclude that there is a biological imperative to the evolutionarily prudent "incest taboo."

Whether pheromones have wafted from afar or made their way to the chemoreceptors of the VNO from the immediate vicinity; and if there is genetic compatibility between the producer and receiver of the pheromones; and finally if the "I" functions of both parties are agreeable then sexual behaviors take place. The many pattern generators that are associated with sexual intercourse and other such interactive behaviors are part of a generalized (or global) control mechanism. Sexual behavior involves the entire nervous systems of the participants. Both the autonomic nervous system, which controls involuntary sexual responses such as erection, lubrication, increased breathing and heart rates as well as well as the somatic nervous system, which is involved with sensory information and voluntary actions, are both fully engaged. Afferent loops are formed between the sensory information being relayed from the skin, genitalia, etc. along the spinal cord to the brain. And efferent loops form between the brain (limbic system and hypothalamus) send messages along the spinal cord to the motor neurons in muscles and glands. (11)

While the sexual activity is an expected consequence of pheromone releaser and primer effects there are subtler effects as well. The presence and close interaction between men and women have definite influences upon women's menstrual cycles from menarche to menopause. It has been observed that both boys and girls who attend single sex boarding schools enter puberty later than do students in co-ed institutions (2).

And Dr. Winnefred Cutler of the Athena Institute in Chester Springs, PA (12) who has done extensive research regarding human pheromones discovered that the presence of men's pheromones have measurable and beneficial effects upon the menstrual cycles and reproductive and general health of women. Dr. Cutler concluded from studies conducted in 1979 and replicated 1986 and 1991 that regular (weekly) sexual relations with men regulated and optimized menstrual cycles and fertility. She contends that it is contact with the male pheromones contained in men's sweat, saliva and semen (13) that is essential. Higher estrogen levels were measured during the luteal phase of the cycle (days 14-16) in women who had weekly sexual relations. High estrogen levels have been found to afford stronger bone density, cardiac health and better mood and memory. Dr. Cutler found the estrogen levels and length of luteal phase of women who were celibate or engaged in only sporadic sex to be subfertile. She concluded that; "These women are likely to be the ones most vulnerable to fibrocystic breast disease, uterine cancer, and other maladies (14).

But as I can attest, having grown up in a household with a mother and two sisters, it is not only exposure to male pheromones that effects women's menstrual cycles. A headline making article published Nature (vol. 229, pp. 244-245, 22 January 1971) confirmed that which my mom, middle sister and I had already discovered. Martha McClintock, then an undergraduate at Harvard published a study showing that women who live together menstruate at the same time (15). However, by the time my youngest sister reached menarche (her periods began) she cycled alone as my middle sister and I had moved out and mom was going through menopause. And in 1998 in "Nature, vol. 392, pp. 177-179, 12 March 1998," McClintock, now a professor at University of Chicago published a study confirming pheromones to be the cause for this phenomena (16). In my present household my teen-age daughter and I experience this synchronization.

But now that I am age 39+ I have begun to think about changes that happen to women in their forties. "During this period, some women increase their estrogen levels to new lifetime highs; others start an unequivocal decline, and still others vary from month to month" (17). Research done at The Athena Institute by Dr. Cutler has also shown that regular, at least weekly, sexual relations for women in their forties can help preserve higher levels of estrogen, thereby allowing women to "age more slowly (including later onset and milder menopause)" (12). She further contends that those regular doses of male pheromones "will decrease the symptoms associated with menopause, such as hot flashes and depression" (17) when women do stop ovulating and menopause does begin.

In light of Dr. Cutler's research and my personal preferences, I have reached the definitive conclusion that I would like to continue to risk an occasional migraine and keep my estrogen levels high. It is clearly in my best interest to do so therefore I'll try to maximize the accessibility of my pheromones. And somehow I suspect that I'll probably will be able to enlist my husband's assistance by way of exchanging pheromones with me. This sharing will thereby maintain the density of my bones and health of my cardiovascular and other parts of my nervous system. And I suspect that this will be equally beneficial to his health and well being.

WWW Sources

1) Migraine triggers

2) Scents, Sex & Pheromones: The Findings of Aroma Research

3) Environmental Estrogens and Other Hormones

4) The Menstrual Cycle: A Beautiful Pattern

5) BDS1 Study Section 5: Endocrines and Reproduction

6) Men Respond to the Scent of a Woman New Scientist 7 Sept 1996


8) The Molecular Logic of Olfaction

9) The Vomeronasal Organ: Florida State Neuroscience

10) The Science of Love

11) How the Nervous System Works During Sexual Intercourse

12) Athena Institute: Discoveries by Dr. Winnifred Cutler

13) Human Male Sweat Extract Sends Strong Message

14) Love Cycles: The Science of Intimacy

15) The Museum of Menstruation and Women's Health

16) New Evidence Shows That Pheromones Influence Menstrual Cycles

17) Wellness in Women After 40 Years of Age: The Role of Sex Hormones and Pheromones

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This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

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