How Our Sense Of Smell Makes Us Fall In Love And Stay In Love

In college, I had a huge crush on a guy who I thought smelled incredible.

His scent -- whatever combination of body odor, musk and deodorant it was -- was not only intoxicating but made me feel like I was on the highest dosage of the most potent psychedelic drug, turning my head fuzzy and my heart whimsical and everything around me into the brightest of colors.

Scent is a powerful, powerful thing.

Interestingly, though, after I stopped having a crush on him, he smelled completely differently.

The heady, stimulating scent I'd loved when I had feelings for him were replaced with... something else. Something, dare I say, kind of bad.

Did the way he smelled really indicate something about how I felt about him? Or did he just coincidentally switch deodorants that week?

Two years ago, Tim Dowling of The Guardian documented his experience in a genetics lab during which he tested his and his wife's DNA to see if they were compatible.

His curiosity arose in an attempt to prove or disprove the old adage that you can literally "smell" compatibility.

Apparently, human beings are capable of sniffing out certain parts of our potential partners' DNA that make up their immune system, called major histocompatibility genes (MHC), to determine whom we're compatible with.

We tend to be drawn to people whose MHC compositions are different from ours so that the immune system of our offspring covers as many diseases as possible.

The idea that our scent is connected to our tendency to be drawn to certain people with certain MHC compositions is based on a famous study that suggests women prefer the scents of T-shirts worn by men whose MHC compositions were different from theirs and, contrarily, think the scents of T-shirts worn by men with similar MHC compositions smell unpleasant.

It turns out that Dowling and his wife were indeed compatible: Their MHC compositions were vastly different.

Looks like they sniffed right.

Dowling's experience is a reflection of how smell really does work to help us find our partner.

And while it's probably not the only way we choose our soulmate, it's one of those factors most people might not even consider.

In addition to helping us find a partner, our sense of smell helps us maintain the connection we establish with that person, too.

Another study suggests that when a woman is not in love, she's pretty good at recognizing the unique scents of her boyfriend, her male friends and her female friends.

But when she is in love, her ability to identify her male friends' unique smells decreases. 

The more attached she feels to her partner, the less she's able to identify the smells of other men, who might be considered other suitors with whom to cheat or to date down the line if she and her boyfriend break up.

Our sense of smell literally prevents us from sniffing out alternate partners while we're dating someone else to protect the monogamy of our relationship.

It also appears to keep us pining for our ex-partners if we're still in love with them after we break up, so until we genuinely fall out of love with our partners, their scent will draw us to them.

Besides our natural scent, perfumes and colognes add complexity to all of these feelings associated with smell.

Perfumes and colognes have strong connections to memory.

If, for example, you've ever smelled Axe body spray after seventh grade, you probably found yourself transported back to middle school gym class during which you, say, got knocked out of dodgeball in the first round.

Using a plethysmograph, a device that measures changes in volume of different parts of our body, researchers at the Smell and Taste Treatment and Research Foundation in Chicago asked men to sniff 30 different fragrances.

They found that every single fragrance caused the plethysmograph to measure an experience of increased blood flow within those tested.

In other words, every single fragrance aroused them.

But "arousal" didn't necessarily have a romantic or sexual connotation, researchers said. It could have been that a scent simply relaxed them or made them think of their mom.

Certain fragrances might give us pleasure (or displeasure) because they remind us of a certain time or person in our life, like a late grandparent, a fresh batch of cookies or the person who broke our heart.

Scientists suggest, however, that the scent more likely to evoke sexual feelings is one that puts you in a good mood.

So, maybe the person who possesses your opposite MHC composition, who also just so happens to be wearing a fragrance that makes you happy, is your soulmate.

Perfumes and colognes smell differently on everyone.

They react differently on everyone's skin, so your body temperature and biological makeup determines how a scent will uniquely reveal itself on you.

Which means maybe, just maybe, it's that perfectly unique combination of a fragrance and a natural scent that makes another person smell intoxicating to us.

And maybe my crush really did change his deodorant, and the new deodorant reacted differently on his skin and made his smell change, thereby making me less attracted to him.

I guess our opposing MHC composition wasn't enough. We weren't really that compatible anyway.