Sexpert: Feb. 23, 2012

Dear Sexpert,

I’ve heard there are some really weird side effects to birth control, like changing whom you find attractive. What’s going on here?

—Curious about Birth Control

Dear Curious,

First, let’s talk a little about how birth control works. In general, there are two broad categories of birth control: barrier and hormonal. Barrier methods simply prevent sperm from getting to the egg. These methods include male condoms, female condoms, diaphragms, etc., and some can also be used to prevent many STIs. On the other hand, hormonal methods, such as the pill and the patch, function by disrupting the woman’s reproductive cycle. Because hormones are very important to many of the daily functions of the body, altering their levels can sometimes have unintended side effects. This is not to say that hormonal contraception should be discouraged, but rather that a person should be well-informed, as with any medication, before starting a regular regimen.

Attraction and love are mysterious phenomena that people have been thinking about for centuries. Biology offers one intriguing perspective on them. For example, according to researcher Rachel Herz at Brown University, smell is the most important factor in finding someone attractive. A person’s natural odor is determined by a segment of DNA called major histocompatibilty complex, which also dictates how the body fights disease. The researchers argued that people unconsciously look for mates who have MHC different from their own in order to have offspring with stronger immune systems. Since saliva often contains MHC, research at the University of Bonn has indicated that a first kiss seems so important to a future sexual relationship because it serves as a test to see if your offspring with this person will be healthy, information that will then compel or dissuade you from pursuing sex.

So, how does this mechanism for choosing a sexual partner relate to birth control? Although different hormonal birth controls work in different ways, the most common disrupt the endocrine system so that the body “thinks” it’s pregnant and stops ovulation. With their bodies in this state, women may find themselves more attracted to people with similar MHC as opposed to people with different MHC.

According to this theory, a woman on hormonal birth control may be attracted to someone whose MHC is similar to hers, when in fact she is more compatible with someone with different MHC. This may be to blame for the high divorce rate: Women find men while on hormonal birth control; then, after they marry, they stop the birth control and find they are not sexually attracted to their husband. Because of this, Herz suggests women use an alternate form of birth control for a time before committing to a person, just in case she is not attracted to him while her endocrine system is not being disrupted.

As always, while it is good to keep yourself informed about how any medicine works, this does not replace advice from your doctor or a medical professional and should not be taken as supporting or dissuading any specific medical choices. As can be expected, the science of something so complicated as sexuality and attraction is the subject of much debate, and clearly there is much more than just smell that brings two people together. If you have further questions about birth control and how it affects your body, be sure to make an appointment at UHS where professionals can guide you through the difficult waters of the medical, sexual, social and scientific aspects of birth control.

— The Sexpert

The Sexpert is written by a team of peer sexual health educators and fact-checked by University health professionals. You can submit questions to sexpert@dailyprincetonian.com. Don’t be shy!