With the number of colognes, perfumes (thank you Britney and P. Diddy), deodorants and body lotions available on the market, you would think fragrance was the number one determinant of sex appeal and relationship success. Maybe, but probably not, says science. Pheromones, chemicals that travel through the olfactory system to the brain, can trigger either a biological or behavioral response, and may account for changes in libido. But this does not necessarily provide an explanation as to why you find one person more appealing than another. "There is some research that says pheromones could play a part in attraction, but it's more complex than that. It's usually sight," that triggers attraction, says Palmer. And often, people are attracted to the stereotypical standards of beauty, she says.