#Love & Sex

The Science of Sex: Does the Nose Know?

by Brie Cadman

The Science of Sex: Does the Nose Know?

Most women have had the mysterious experience of being turned on by a partner’s smell. A friend of mine once told me her ex-boyfriend’s scent made her feel “safe and drawn to him,” and that his smell was so distinct and attractive that even after a sweaty workout, she found him appealing. Though personality and looks definitely play a part in initial attraction, smell may play a larger role than we suspect. That inexplicable “chemistry” you feel with someone who may not fit your normal dating profile? It could be a subconscious scent drawing you to him or her.

Studies have found that how a person smells gives us clues to their genetic make-up, and thus, their potential to be a compatible mate. On a subconscious level, decoding a scent gives us a powerful tool to ensure our kids will be healthy, and our orgasms will be plentiful.

The first study to indicate that chemical signals play a role in attraction was conducted by Claud Wedekind over a decade ago. Forty-four men wore the same T-shirt for three days. They refrained from deodorants and scented soaps so they wouldn’t interfere with their natural smell. Women then sniffed the shirts and indicated which ones smelled the best to them. By comparing the DNA of the women and men, the researchers found that women didn’t just choose their favorite scent randomly. They preferred the scent of man whose major histocompatibility complex (MHC)—a series of genes involved in our immune system—was most different from their own.

Researchers knew to look at the MHC because of its importance in animal’s sexual preferences. In mice, it has long been known that MHC not only helps ward off infection, but it also plays a role in scent and mate selection.

From an evolutionary perspective, choosing a mate with a different immune system makes survival sense. Kids of parents with different immune genes are more likely to be disease-resistant and are therefore more likely to survive. The women in this study also reported liking the scents that reminded them of their current or previous boyfriends, showing that MHC attraction is consistent. And because MHC profiles differ greatly from one person to the next, there is no universally “good” smell. One woman’s Romeo was another woman’s raunchy.

Further studies have built upon this initial finding of mate preference. It turns out that women are most attracted to men that have an MHC profile similar to their fathers. That is, they don’t want a mate with an identical genetic make-up, but they also don’t want one that has no overlapping genes at all. By doing this, women can avoid in-breeding (which can result in genetic defects) and complete out-breeding (which can dilute robust genes).

A genetically complimentary mate means more than just initial attraction, however. It also leads to more female orgasms, better chances of conception, and an improved sex life. And the attraction based on scent isn’t just reserved for heterosexual couples. Gay men and lesbians respond as would be expected to body odors, but to the same sex.

An interesting exception to the MHC attraction is for women taking the pill. Wedekind found that pill-takers responded in almost the exact opposite manner than would be expected. Because the pill tricks your body into thinking it is pregnant, it chemically alters your sense of attraction. Instead of finding the scent of genetically dissimilar men attractive, women on the pill found the scent of men with MHC’s similar to their own to be attractive.

This may be because when a woman is pregnant, she isn’t looking for a new mate, and may benefit from being around kin, or those with a similar genetic make-up. But, because scent can be such a powerful indicator of a mate that is biologically compatible, what does this mean for women on the pill? Research has shown that picking a mate whose MHC is too similar to your own can result in higher rates of miscarriage and relationship difficulties like infidelity. Are contraceptive takers sabotaging their innate ability to pick a proper mate?

Though certainly the scent of a man can be a powerful indicator of genetic compatibility, it certainly doesn’t dictate everything. If a woman falls in love with a man, and then begins the pill, she’s not likely to lose interest; love may be more powerful than the initial scent connection. And there are certainly other factors at play than just scent. Like most biological responses, mate preference and sexual attraction is much more complex than just how we smell. Because our scent communication acts at a subtle level, we have to get close enough even to detect it; that is, there needs to be a reasonable amount of physical or intellectual attraction in the first place. Although there is a new internet dating-site based on the MHC smell basis, scientificmatch.com, they still require users to fill out the normal things that most people base their compatibility on: age, hobbies, interests, income, etc.

Our noses may help us find the mate most suited to us, but it’s ultimately up to our minds to decide whether or not we like what we’ve sniffed out.