There are plenty of things that can make us do a 180 when it comes to sexual attraction: getting mansplained on a first date, realizing your new bae wears pleated khakis almost exclusively, seeing your partner clip his toenails in bed, and… your birth control pill?

Yep, turns out birth control can have a major impact on who you’re attracted to. It comes down to Major Histocompatibility Complex (MHC) genes. “The theory goes that we are attracted to the scent of people with genes in the Major Histocompatibility Complex (MHC) that are different from our own,” explains Eva Martin, MD, the CEO and Founder of Elm Tree Medical. “From an evolutionary standpoint, this makes sense because it would reduce the risk of expression of deleterious recessive genes.”

Yep, turns out birth control can have a major impact on who you’re attracted to.

Naturally, we do pretty well avoiding partnering up with people with MHC genes similar to our own — unless we’re taking hormonal birth control. In the now-classic t-shirt study of 1995, researchers collected DNA samples from men and women and asked the men to wear cotton t-shirts for two nights. The shirts were then collected, and the women were asked to rate them for intensity, pleasantness, and sexiness. Women not taking oral contraceptives thought the men with a dissimilar MHC smelled more pleasant than men with a similar MHC, the researchers explained in the Proceedings of the Royal Society of London journal.

A larger 2008 study got similar results when they tested women’s preferences before and after starting the pill. Once on the pill, women shifted from a preference for men with dissimilar MHC genes to men with similar MHC genes. “Essentially, the natural ability to discriminate between similarity and differences in MHC composition is disrupted, causing women’s preferences to shift and be more sexually attracted to the odor of males with MHC genes more similar to themselves,” explains Jennifer Verdolin, PhD, scientist and author of Wild Connection: What Animal Courtship and Mating Tell Us about Human Relationships.

Translation? On the pill, we go for completely different men than we would off it — and that could be bad news down the line. “This shift could be costly if it results in choice of more MHC-similar partners,” the study’s researchers write. In particular, MHC similarity in couples may lead to increased risk of miscarriage and longer lengths of time in between births for those with multiple children, the study found — and even to the breakdown of the relationship if odor perception plays a part in maintaining attraction. (So far, these studies have only looked at heterosexual attraction.)

On the pill, we go for completely different men than we would off it — and that could be bad news down the line.

And if you were on the pill when you met your current partner, you might be in for a few surprises if you go off it, a 2014 study suggests. Researchers examined 118 newlyweds for four years, asked them questions about relationship satisfaction and oral contraceptive use along the way. Women who stopped taking a hormonal contraceptive and became less satisfied with their relationship tended to be partnered up with husbands judged as less attractive. Women who were more satisfied with their relationships after dropping the pill had husbands who were judged as good looking. “In other words, a partner’s attractiveness plays a stronger role in women’s satisfaction when they discontinue hormonal contraceptives,” explains the study’s lead author Michelle Russell. Another study found that women who went — and stayed — on the pill throughout a long-term relationship, as well as women who had never used the pill, reported greater sexual satisfaction than women who began or stopped use during the relationship.

Considering that 82% of women ages 15-44 have used the pill at some point, this all seems like a pretty big deal that we should all start panicking about ASAP, right? Dr. Martin doesn’t think so. For one, some of these studies are in a laboratory setting and rely on t-shirts, she says. Plus, this research is focusing on MHC similarity, not types of people. “There is so much at play in a relationship between two people that I think it is too simplistic to say that starting or stopping the pill causes a woman to stop feeling attraction to her partner or vice versa,” Dr. Martin says.

Yes, the research suggests that hormonal birth control can be a major player in your love life — but you may not want to toss your pills based on these studies alone. Consider all of the possible effects of the pill, good and bad, when deciding if it’s right for you… and consider that MHC similarity alone is unlikely to tank a happy, sexually satisfying relationship. Mansplaining, pleated khakis, and toenail clippings in bed, on the other hand…

Diana Vilibert is a freelance writer and copywriter living in Brooklyn, NY. She loves flea markets, martinis, to-do lists, traveling, and wearing leggings as pants. You can see more of her writing at www.dianavilibert.com and follow her on Twitter at @dianavilibert.