Physical attraction may be as old as time, but new studies are beginning to uncover the science behind sex appeal.

Unexpected factors—like smell, facial symmetry, voice pitch, financial stability and kissing prowess—just might have more to do with your choice of mate than anyone ever expected. Discover the evolutionary explanations.

A spritz on the wrist. A dab behind the ears. Many men and women spend a lot of time—and money—searching for a signature scent that attracts the opposite sex. Little do they know, these lotions and potions actually mask the natural odors scientists say potential mates find most appealing.

Karl Grammer and Elizabeth Oberzaucher, researchers who study how the human scent influences sexual attraction, found that when women are ovulating, they produce pheromones called copulins. Copulins have a distinct smell, which Elizabeth describes as "butter gone off."

When a man gets a whiff of copulins, his testosterone levels rise. As a result, he secretes androstenone, an odor that repels women who aren't ovulating.

Sex therapist Dr. Laura Berman says science and evolution plays a larger role in attraction than people might think. "We are capable of discerning 10,000 different scents consciously," she says. "But then there's a whole realm of unconscious scents that we're not even aware that we're smelling."

In one recent study, Dr. Berman says researchers had women smell men's T-shirts. The women were most attracted to the shirts of men whose major histocompatability complexes (MHC) differed from theirs. MHC is a collection of genes that are related to immune systems. "We unconsciously want to mate with someone who has a different immune system than ours," Dr. Berman says. "That helps with the survival of our offspring."


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