When I read about Smell Dating, a service that matches people by sending swatches of T-shirts worn without deodorant for three days and three nights, I wondered if we'd finally crossed the final dating frontier.

But, as it turns out, smell matters, especially when it comes to sexual chemistry, and there's a biological reason why.

"Body odor has a way of unconsciously letting the sniffer know you have differing genes," says Dr. Gail Saltz, an associate professor of psychiatry at the New York Presbyterian Hospital Weill-Cornell School of Medicine, bestselling author and the host of "The Power of Different" podcast.

But what if other issues affect smell and thereby throw off this built-in system?

For example, illnesses like diabetes, stomach ulcers and gastritis as well as mouth and gum diseases can alter your natural body odor, Saltz says.

"Being on birth control can also impede the sniffer's ability to detect those genetic differences," she adds. "Perfumes can mask body odor and thereby throw off the system as well."

And, what if underneath all that perfume or cologne, you find someone's smell to be bothersome?

"A smell issue can be turned around depending on the cause," Saltz says. "If it's because the person eats spicy or garlicky foods, that's an easy fix. If the cause is a detergent that offends when mixed with body odor, that, too, can be fixed."

A man finishes a glass of wine The food and drink we consume influences our scent, but that's only part of the story. (Photo: Sergiy Palamarchuk/Shutterstock)

What science has sniffed out

When it comes to the relationship between smell and attraction, the research is somewhat conflicting.

For example, some studies suggest that women are attracted to the scent of men with higher testosterone, particularly during the time of the month when they're most fertile, says David Bennett, a dating and relationship expert behind The Popular Man website. In other studies, women rated men more attractive when the man's face was associated with a pleasant scent.

There's more: From an evolutionary perspective, smell serves as a method of detecting genetic compatibility particularly as it applies to immunology and having healthy offspring. In other words, the theory is that good smell compatibility will increase the likelihood that you can conceive and that your offspring will be more immune to diseases.

"That's why I think the concept of 'smell dating' is rather a misnomer," says Dawn Maslar, a biologist whose new book, "Men Chase, Women Choose: The Neuroscience of Meeting, Dating, Losing Your Mind, and Finding True Love," goes on sale next month. "It’s not really the smell that attracts two people, but rather the picking up of different protein molecules."

Those molecules are officially known as Major Histocompatibility Complex molecules (MHC), Maslar says.

"These MHC molecules are part of our immune system, and we are naturally more attracted to people of opposite immune systems," she says. "This makes perfect biological sense in that if the union of the two individuals produces a child, that child would have a better compliment of immune cells and therefore a healthier immune system."

In the end, just like the eyes, the nose is only part of the attraction one person has for another.

"Why is it that many become attracted to a photo, but the attraction disappears when the meet?" Maslar says. "That's because all your senses come into play to judge attraction when the person is in the room. Therefore, a smell only gives you part of the answer. Things can change once the blindfold comes off."

So what do you do when you meet someone but their smell just doesn't jibe with your idea of an appealing odor?

"If, at the end of the day someone's smell is really a big obstacle, that may be telling you that this was just not meant to be," Saltz says.

How much does smell matter when it comes to falling in love?
Smell plays a large part in attraction, including sniffing out genetic differences and health.