When Enovid, the first birth control pill approved by the U.S. Food and Drug Administration, hit the market in 1960, American women were eager for the option. Previously cleared as a treatment for menstrual disorders in 1957, Enovid was already making the rounds among gynecological practices, with half a million prescriptions doled out ostensibly to regulate periods [source: PBS]. When the pill turned 40 in 2010, an estimated 100 million women around the world were using oral contraceptives, primarily to prevent pregnancies [source: TIME].
Birth control pills prevent pregnancy by inhibiting a woman's ovaries from releasing a mature egg into the fallopian tubes during monthly ovulation [source: Planned Parenthood]. Typically, oral contraceptives combine the hormones estrogen and progestin to maintain a routine menstrual cycle, sans ovulation. In doing so, birth control has granted women greater agency over their bodies and their reproductive systems, allowing them to better manage if and when motherhood happens. As a side effect of reducing the pregnancy risk, the pill also opened the door to greater sexual freedom.
But eliminating ovulation may also affect women's sex lives in more subtle ways, recent studies are starting to show. In the process of tricking a female body into thinking it's pregnant, oral contraceptives may discretely alter heterosexual women's attraction to men and vice versa. Although none of the following five birth control-related reactions pose any direct risk to women, they're fascinating examples of how a single, tiny egg can make a monthly difference.
Research has found that women at their monthly peak of fertility unconsciously engage in certain self-embellishing behaviors, such as shopping and more provocative dressing [source: University of Minnesota]. Evolutionary biologists attribute these ovulation-specific patterns to humans' innate imperative to reproduce. By that logic, when the female body is most primed to become impregnated, it sends out readiness signals to surrounding men and also heightens the woman's awareness of potential suitors.
For instance, psychologists at the University of Trom in Norway tracked women's pupil dilation, a physiological response to attraction, at multiple intervals during their menstrual cycles. Viewing a series of sexually stimulating photographs each time, participants' pupil dilation was most pronounced during the women's ovulatory phase -- unless they were taking oral birth control [source: Laeng and Falkenberg]. Women on the pill demonstrated no such additional stimulation, even in response to a photo of their current sexual partner. Granted, pupil dilation or lack thereof likely doesn't make or break a someone's love life, but it's nevertheless a benign indicator of how hormonal contraception possibly trifles with sexual response.
Sending Mixed Signals
A lingering question about human evolution is what happened to female estrus. In other mammals, estrus is more commonly referred to as being "in heat," the brief window when females can be impregnated. Women, on the other hand, can get pregnant at any point during their menstrual cycles, and -- unlike some other animals, like baboons, which may experience temporarily engorged vulvas -- ovulation comes with no outright physical signs of fertility. At the same time, some evolutionary psychologists suppose that heterosexual men are subconsciously able to detect women's concealed ovulation, as long as they aren't on the pill [source: Pappas].
A trio of University of New Mexico researchers tested that hypothesis in a less-than-academic environment: a strip club. For 60 days, strippers recruited for the study logged their daily tips from customers, along with their menstrual cycle progress. Plotting those data points together revealed a fluctuation in earnings correlated to fertility. During ovulation, strippers took home $335 per shift, compared to $185 per shift during their low-fertility periods [source: Miller, Tybur and Jordan]. However, customers tipped women on hormonal birth control roughly the same amount each day, averaging $80 less than their naturally cycling cohorts [source: Miller, Tybur and Jordan].
Why the paltry pay? Researchers suspect that men instinctively found the naturally cycling, more immediately fertile dancers more sexually appealing [source: Miller, Tybur and Jordan].
Can you hear me now?
Evidence suggests that heterosexual men find ovulating women more visually attractive than women taking oral birth control or au natural women during less fertile menstrual phases. But does ovulation also announce itself with auditory advertisements as well? Yet again, study results lean toward the affirmative. Vocal recordings of women across their menstrual cycle tend to demonstrate tonal deterioration as menstruation approaches [source: Barnes and Latman]. Clinicians have notes cases of premenstrual voice problems among classically trained female singers, for instance [source: Barnes and Latman]. Off-stage, men listening to audio samples of female voices rated the clips captured during women's periods as the least appealing, compared to the sweeter sounds heard from more fertile menstrual phases [source: Pipitone and Gallup Jr.].
Researchers suspect varying levels of hormones and their effect on vocal tissue are responsible for such vocal inconsistencies [source: Pipitone and Gallup Jr.]. For women taking oral contraceptives that deliver a stable dose of estrogen and other hormones, that issue may not affect them. Indeed, one study concluded that oral contraceptives may improve vocal stability over time [source: Amir and Kishon-Rabin]. That said, scientists haven't determined whether that difference portends real-world impacts aside from possibly improved karaoke performances, care of estrogen.
(Not) In the Mood
One of the most ironic hormonal contraceptive side effects for some women is a lowered libido. Indeed, birth control can work too well, in a sense, not only diminishing pregnancy risk but also dampening the desire for sexual intercourse. Anecdotal evidence has long supported this unadvertised side effect, and a growing number of studies have confirmed the rumors. In November 2011, for example, an in-depth survey from Indiana University found that women on hormonal birth control had more trouble with sexual arousal and engaged in sexual activity less frequently [source: Smith].
Sexual dysfunction, such as low sex drive, poor lubrication or difficulty achieving orgasms, isn't uncommon for women regardless of birth control. As many as two in five women report at least one sexual dysfunction; the question is whether the hormones in birth control could be to blame [source: Beal]. Estrogen and progestin contained in the pill might interfere with the body's testosterone production, which doubles as the gas station fueling sex drive [source: Melnick]. Unraveling external hormonal influences from generalized sexual dysfunction remains a hurdle for researchers, but repeated analysis has implicated oral hormonal contraception as a common culprit among women reporting limp libidos.
Choosing Mr. Wrong
Perhaps the most unsettling way birth control tinkers with love lives is that it may steer women toward genetically unsuitable mates. By successfully tricking the body into thinking its pregnant, underlying sexual behaviors follow suit, diverting single women toward more genetically similar men [source: LiveScience]. Why is that potentially troublesome? Although humans tend to practice assortative mating, in which people with similar backgrounds and sociodemographics couple up; genetically, however, opposites attract.
A 2008 study published in the Proceedings of the Royal Society B found that women taking hormonal contraception found men more attractive who had similar major histocompatibility complex (MHC) genes. For naturally cycling women, however, the opposite is true. That's because more dissimilar MHC genes produce hardier immune systems in their offspring [source: Wenner].
That birth control MHC mix-up likely relates back to the body's fake pregnancy. Carrying a child compels women to build a social support system among family and friends rather than seeking out a sexual suitor. Down the road, MHC similarity might spell trouble for a relationship, according to a separate study published in Psychological Science. In it, women in MHC-alike pairs were less sexually satisfied and more likely to cheat [source: Wenner]. The research didn't divulge women's birth control habits, but ditching the pill could reignite that muffled MHC sense and sidetrack their sexual attention away from their genetically familiar partners.
Doctors aren't putting a halt on prescriptions for the pill, however, and for a lot of women, it might still be their best option for preventing unwanted pregnancy. After all, every medication has its benefits and drawbacks. Until scientific data conclusively proves otherwise, birth control is perfectly safe and good for women's love lives -- and possibly their vocal cords and shopping habits as well.
Mom or mother-in-law live with you and the hubby? She might be interfering with your reproduction rates. Find about this new study at HowStuffWorks.
- Quiz: What goes on in your brain when you're attracted to someone?
- The Look of Love: Top 5 Signs of Physical Attraction
- How the Birth-control Pill Works
- How the Male Birth-control Pill Will Work
- How Love Works
- How Aphrodisiacs Work
- How Flirting Works
- How Kissing Works
- How Planned Parenthood Works
- Is love at first sight possible?
- Amir, Ofer and Kishon-Rabin, Liat. "Association Between Birth Control Pills and Voice Quality." The Laryngoscope. Jan. 03, 2009. (Jan. 24, 2012) http://onlinelibrary.wiley.com/doi/10.1097/00005537-200406000-00012/full
- Barnes, Larry and Latman, Neal. "Acoustic Measure of Hormone Affect on Female Voice During Menstruation." International Journal of Humanities and Social Science. Vol. 01, No. 03. March 2011. (Jan. 24, 2012) http://www.ijhssnet.com/journals/Vol._1_No._3%3B_March_2011/2.pdf
- Beal, Jennifer. "Hormonal contraceptives associated with higher risk of female sexual dysfunction." EurekaAlert! May 04, 2010. (Jan. 24, 2012) http://www.eurekalert.org/pub_releases/2010-05/w-hca042910.php
- Cell Press "Unnatural Selection: Birth Control Pills May Alter Choice Of Partners." ScienceDaily. Oct. 07, 2009. (Jan. 24, 2012) http://www.sciencedaily.com/releases/2009/10/091007124358.htm
- Laeng, B. and Falkenberg, L. "Women's pupillary response to sexually significant others during the hormonal cycle." Hormonal Behavior. November 2007. (Jan. 24, 2012) http://www.ncbi.nlm.nih.gov/pubmed?term=Women%27s%20pupillary%20responses%20to%20sexually%20significant%20others%20during%20the%20hormonal%20cycle
- LiveScience. "The Pill May Alter Sex Partner Preferences." Oct. 08, 2009. (Jan. 24, 2012) http://www.livescience.com/9744-pill-alter-sex-partner-preferences.html
- Macintosh, Zoe. "The Pill Linked to Low Libido in Women." LiveScience. May 06, 2010. (Jan. 24, 2012) http://www.livescience.com/9901-pill-linked-libido-women.html
- Melnick, Meredith. "Study: Does the Pill Lower Sex Drive?" TIME. Nov. 29, 2010. (Jan. 24, 2012) http://healthland.time.com/2010/11/29/study-does-the-pill-lower-sex-drive/
- Miller, Geoffrey; Tybur, Joshua M.; and Jordan, Brent D. "Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus?" Evolution and Human Behavior. Vol. 28. 2007. (Jan. 24, 2012) http://www.unm.edu/~gfmiller/cycle_effects_on_tips.pdf
- Pappas, Stephanie. "Booty Call: How to Spot a Fertile Woman." LiveScience. Oct. 17, 2010. (Jan. 24, 2012) http://www.livescience.com/10828-booty-call-spot-fertile-woman.html
- PBS. "Timeline: The Pill." American Experience. (Jan. 24, 2012) http://www.pbs.org/wgbh/amex/pill/timeline/timeline2.html
- Pipitone, R. Nathan and Gallup Jr., Gordon G. "The Unique Impact of Menstruation on the Female Voice: Implications for the Evolution of Menstrual Cycle Cues." International Journal of Behavioural Biology. Dec. 22, 2011. (Jan. 24, 2012) http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.2011.02010.x/abstract
- Planned Parenthood. "Birth Control Pills." (Jan. 24, 2012) http://www.plannedparenthood.org/health-topics/birth-control/birth-control-pill-4228.htm
- Smith, Nicole. "Not your mother's birth control, same troubles." Indiana University. EurekaAlert! Oct. 31, 2011. (Jan. 24, 2012) http://www.eurekalert.org/pub_releases/2011-10/iu-nym102811.php
- TIME. "A Brief History of Birth Control." May 03, 2010. (Jan. 24, 2012) http://www.time.com/time/magazine/article/0,9171,1983970,00.html
- University of Minnesota. "Ovulating women unconsciously buy sexier clothing to outdo attractive women." ScienceDaily. Aug. 04, 2010. (Jan. 24, 2012) http://www.sciencedaily.com/releases/2010/08/100804122711.htm
- Wenner, Melinda. "Birth Control Pills Affect Women's Taste in Men." Scientific American. Dec. 05, 2008. (Jan. 24, 2012) http://www.scientificamerican.com/article.cfm?id=birth-control-pills-affect-womens-taste