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Love’s Chemistry and the Pill: are they at odds?
By Abigail Jeffies
When we fall in love, there is mystery, excitement, romance, obsession, anxiety, anticipation, and suspense—to name but
of few of love’s many undeniable, though unscientific, manifestations. But when we are lucky enough to find a mate who loves us
back, we say there is chemistry.
Though humans have long lived by this truth, scientists are only just beginning
to uncover the actual mechanisms that drive the mating game. One surprise: the
use of oral contraceptives may throw a wrench into them.
The scent of attraction
Fertility cues in men (deep voice, athletic physique, and take-charge, hunky kind of
dominance) and women (feminine face, curvy figure, and alluring voice) are just plain
sexy, but they also tell us on a subliminal level that if we mate with this person, we are
more likely to have strong, healthy off spring. There may also be invisible cues that tell
us when a biologically fit or fertile potential mate is at hand. Pheromones, chemical
signals that trigger a natural response in another member of the same species, may
attract humans to one another sexually through smell.
“There are millions of things that are going on with different chemicals that we perceive
and don’t perceive,” said Chris Kilham, Explorer in Residence at the University of
Massachusetts, Amherst, and author of Hot Plants: Nature’s Proven Sex Boosters for
Men and Women. “So much has to do with the invisible. We have all kinds of
mechanisms that we probably haven’t figured out yet that relate to the sense of smell,
and they have a great deal to do with biological attraction.” Studies have found
numerous cause-and effect relationships that indicate body odor can impact
mood, sexual attraction and the release of a hormone that affects the timing of a
woman’s menstrual period. It has also been observed that a woman’s hormonal status can affect her choice of clothing
and the pitch of her voice.
One study found that women prefer the scent of T-shirts worn by men whose
major histocompatibility complex (MHC)—a set of genes that plays an important
role in the immune system—is most dissimilar to their own. Should they mate
with these MHC dissimilar men, they would have a greater chance of producing
off spring with stronger immune systems. “It makes perfect sense that we would
have a mechanism that compels us to mate with someone who is not
MHC-similar, because it’s desirable to avoid inbreeding,” said Alicia Stanton,
MD, Chief Medical Officer of BodyLogicMD and author of Hormone Harmony.
The “divorce” pill?However, the T-shirt odor assessment results were
reversed when the women studied were taking hormone-based oral
contraceptives, suggesting that body scent and hormonal status
influenced mate selection. These women preferred the scent of men who
had MHC similar to their own, as would a relative.
So, does this mean that if a woman is on the pill she might be attracted to
the wrong guy? Or worse: if she’s on the pill when she finds Mr. Right,
then marries him, then stops taking the pill to start a family, will she wake
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up one day and find she’s no longer attracted to him?
“The studies are controversial. The premise that the birth control pill makes women choose their mates less wisely is
not a given,” said Joseph Walsh, MD, Assistant Clinical Professor at the University of Connecticut Health Center in
Farmington. “The trouble with a lot of these studies in evolutionary psychology is that there are associations but no
causation. It’s very difficult to do a randomized study where you have one group on placebo, one group on the pill, have
them choose mates and then reverse it and see what happens with mate selection.”
Does a man read the chemical signals sent by a woman differently when she is taking
the pill? A University of New Mexico study of professional lap dancers found that those
who were not taking hormonal contraceptives earned more money during the most
fertile (ovulating) phase of their menstrual cycles compared to times of low fertility.
Those who were taking hormonal contraceptives (which stops ovulation) did not have
higher mid-cycle earnings, suggesting that men are somehow more attracted to ovulating
The mystery of human pheromones
A popular theory is that pheromones account for chemical sexual attraction.
Pheromones have been found to exist in non-human mammals including
chimpanzees and baboons, but they have not yet been isolated in humans. And
humans may no longer be wired to receive and process pheromones.
The vomeronasal organ, a structure in the nose of many vertebrates that
receives pheromonal messages and sends them to an olfactory region of the
brain, is non-functioning in adult humans.
Though the “how” of the pill’s effect on mate selection is not yet understood, one possible “why” might be based less on
pheromones and more on sociology. Oral contraceptives mimic pregnancy by providing a woman with high levels of the hormones
estrogen and progestin. Th is tricks the ovaries into shutting down egg production, which prevents conception, but it may also
trigger a basic survival strategy. “It has been proposed that women on the pill prefer the scent of a man who is MHC-similar
because pregnant women want to be with someone safe and supportive, such as a relative, while they are vulnerable,” said Mache
Seibel, MD, Reproductive Endocrinologist and Professor at UMass Medical School in Worcester. Mary Jane Minkin, MD, Clinical
Professor of Obstetrics and Gynecology at Yale University School of Medicine in New Haven offered another hypothesis: “The
ovaries make testosterone. Women are sensitive to a lack of testosterone. When the pill causes ovulation to stop this also means that
testosterone production stops, and this might affect libido, thereby causing women on the pill to prefer platonic relationships.” That
said, Minkin noted that libido is “hugely complex” in women. “It’s very different from libido in men for many reasons. My patients
are so terrified of unwanted pregnancy that any loss of libido caused by the pill is compensated for by the sense of protection from
pregnancy. When they’re on the pill, they’re ready for sex,” she said.
The skinny on hormones and birth control
There are several alternative methods of contraception that do not mimic pregnancy.
“Condoms, mechanical methods like diaphragms, the copper-containing intrauterine
device (IUD), and natural family planning prevent pregnancy without using hormones,”
Walsh said. “The progesteronebased IUD secretes hormone but at such a low level that it
would probably not have any effect on mate selection, if this in fact happens.”
Even if a woman is not taking the pill, she may be using a hormone-based birth
control method. “The patch, the NuvaRing, the Depo-Provera 3-month injection,
the single rod implant – these methods are all hormonal, but some of them
contain only half of the hormone that is in the pill,” Walsh said. “In most cases
the pill contains a combination of estrogen and progestin. Implanon and
Depo-Provera contain only the progestin component.
This does reproduce a pregnancy state, but we don’t know what effect this has on mate selection.” The hormones in
contraceptives are not structurally the same as the hormones our bodies make naturally. “Their shapes are not going to fit into the
body’s receptors as well as our own hormones would,”
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Stanton said. “The pill contains progestin (synthetic progesterone), not the natural progesterone that is elevated when a woman is
pregnant, and this difference can cause side effects like weight gain, water retention and depression. This is because progestin
does not act in the body the same way that progesterone does. The body is confused. It thinks there is some
progesterone on board because the pill is affecting some of the progesterone receptors, but not all. The way the pill
appears to disable a woman’s ability to discern MHC may be one of these side effects we don’t yet understand.” Stanton
treats male and female patients with symptoms of hormonal imbalance using bioidentical hormones – soy- and yambased hormones
that have been tweaked in a lab to be molecularly identical to human hormones. “Your body doesn’t know the difference,” she said.
So far, there are no contraceptives available that use bioidentical hormones.
What’s the take-away?
Human pheromones may or may not be imperceptibly advertising fertility, attracting potential mates, or guiding a
pregnant woman to sanctuary among family. They may or may not be turned on and off by synthetic hormones in birth
control pills. Whether there is any link between hormones and pheromones is “the $64,000 question,” Seibel
said. “Almost every woman who has lived in a dorm knows that women who group together menstruate together,”
“That is believed to be a result of synchronizing pheromones. It’s not a quantum leap to believe that some olfactory
message could attract potential mates.” Not a leap, perhaps, but definitely a stretch. “To put the studies that have been
done into clinical use, to suggest that women not choose the birth control pill in order to avoid the MHC problem, would
be premature,” Walsh said.
At the end of the day, sexual selection is more than hormones and pheromones. “The more people know each other
and care for each other the more these become enhancers rather than selectors,” Seibel said.
Last Updated (Tuesday, 09 March 2010 16:34)