Women On The Pill Will Pick The Wrong Mate
 
The way your date smells matters more than looks. No matter how attractive people appear, the way they smell is a far better predictor of chemistry. That's because your nose is a keen instrument for smelling a genetic blueprint called the major histocompatability complex, or MHC. 
 
When certain people smell good, that means their MHC is complementary to your own, which means you'd produce strong offspring if you tried. When someone's MHC is not a good match to your own, you won't like the way they smell, and will probably move on.
 
Without going too deep into science specifics, a groundbreaking 1995 study conducted in Switzerland by a researcher named Claus Wedekind (who has since returned to studying animals-fish, to be exact) revealed women find the scents of men attractive when the man's immune system genes are most compatible with her own. Well-matched immune system or multi-histiology complex (MHC) genes make for healthy babies, and "Goldilocks-like" pairing is ideal: not too similar but also not too distinct.
 
However, something very interesting was also found. Both the Swiss study and replicated versions have proven that women on hormonal birth control-those studied were all on the Pill, not localized hormonal options like the NuvaRing or IUDs-are attracted to the scent of men whose MHC genes are most similar to their own. In other words, men who are bad DNA matches. So what gives?
 
The Pill and other hormonal birth control prevent ovulation. This signals to a woman's body that she's pregnant, a state in which a woman is better off being around smells that indicate family-those with DNA similarity-for protection rather than scents with less DNA similarity, which indicate potential suitors. As Brown University professor and one of the world's leading scent researchers, Rachel Herz, puts it, "[The Pill] hormonally mimics a state of pregnancy and kin is better to be around during this vulnerable period."
 
This research leads to the idea that using their sense of smell, women on the Pill will pick the wrong mate. The hormonal mix in birth control pills confounds the woman's sense of smell, steering her toward men with a genetic blueprint that's not very compatible to her own. So ideally, if you're looking for the perfect guy, you should not use the Pill during your search for Mr. Right.
 
Because of this effect, some have tagged the Pill as "the divorce pill". While both scientists and lay persons have since surmised that this poses both fertility and compatibility risks for couples who meet while the woman is on hormonal birth control, tagging it as "the divorce pill" overstates the effect.
 
"I have seen female patients who are less attracted to their husband and facing fertility issues after going off the pill," says Dr. Diana Kirschner, a clinical psychologist who's been practicing for more than 25 years and the founder of Love in 90 Days workshops. "But there are a lot of other factors that contribute to the lack of desire."
 
Furthermore, as Herz points out, emotional attachment can beget scent attachment, even if the scent is that of cologne or deodorant.
 
"Axe deodorant commercials have a bonanza on their hands," she says. "For women, how a man smells is the most important factor in her sexual attraction after his level of pleasantness." While the Pill can't be blamed for divorce, its effects on scent and attraction are enough for DNA matchmaking sites like scientificmatch.com to turn down female clients who take it.
 
"DNA compatibility doesn't seem to influence how well we get along, how well we play chess or travel together," Herz says. But would she recommend a woman looking to find a reproductively compatible mate stay off hormonal birth control? Yes, absolutely.
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