Study: Birth Control Pill Use Affects Smell

Most women take birth control pills to prevent pregnancy, but oral contraceptive use may have unwanted sexual side effects.

A study appearing today in Human Reproduction found women taking a birth control pill were less sensitive to scents, which may negatively affect their sex drives.

Researchers tested the ability of 60 women not taking the pill to detect six smells at various points in their menstrual cycles. Sense of smell was shown to be most sensitive around ovulation, a time when women are most fertile.

The subjects were then put on birth control pills and their sense of smell was re-tested. After three months of pill use, the increased sensitivity to smell usually seen during ovulation was absent.

Sex and Smell

"After many years of studies on sexuality dysfunction, we found that many factors influence a woman's desire, one of which could be the sense of smell," says Salvatore Caruso, lead author of the study and professor in the department of gynecological science at the Ospedale S. Bambino in Italy.

While the sense of smell and libido have not been specifically linked, there is evidence to support such a relationship.

"There are women who are born without a sense of smell who have no activity in their ovaries," says Dr. David Brinton, a reproductive endocrinologist at William Beaumont Hospital in Royal Oak, Mich. "There is a physiological proximity issue."

In other words, areas of the brain that control both the sense of smell and the ovaries are physically located close to one another. Something that affects one area could conceivable affect the other.

Implications of Pill Use

Other research has uncovered a relationship between the sense of smell and pill use. Research by Steve Gangestad, a University of New Mexico psychology professor, showed that women taking oral contraceptives had no significant preference for the smell of males with symmetrical features vs. asymmetrical features.

Symmetry in features is a measure of attractiveness and genetic fitness. Women not taking the pill preferred the smell of males with symmetrical features during their most fertile time.

"What we found is that the pill may actually upset normal preferences for choosing mates," says Gangestad.

Pill use can also decrease sex drive in some women. However, experts point out that sex drive and choosing a mate are very complex issues that involve many physical and psychological variables.

"A lot of women on birth control pills have a decrease in inhibition which may have an overriding effect," says Brinton.

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