We know that smell is one of the most emotionally powerful senses, triggering vivid memories from even a wisp of a waft. On Stuff Mom Never Told You, Molly and I have discussed how people unconsciously "sniff out" biologically suitable mates with complementary gene pools. A 2009 psychology study from Rice University adds another compelling note to this complex perfume of humans' conscious and unconscious smell responses. fMRI data indicate that heterosexual women's brains can distinguish men's sexy sweat from their neutral sweat, like the kind they work up while chopping wood or bench pressing or doing one-handed push-ups.
The female participants were asked to smell and rate absorbent pads soaked with four different types of odors: sexy sweat (collected while male participants watched an erotic film), neutral sweat, a sex pheromone and a neutral, non-sweat odor. Although most of the women didn't consciously detect much of a difference between the pads' smells, their brains did. As the New York Times reported, "two regions of the brain, the right orbitofrontal cortex and the right fusiform region, responded significantly more to the sexual sweat of men than to any of the other smells."
Interestingly, the hypothalamus -- linked to sexual motivation and behavior -- didn't light up, which means there wasn't any sort of aphrodisiac effect of smelling the sexy sweat. Instead, the findings suggest that our olfactory responses to potential mates are more nuanced than immediate thumbs up or thumbs down appraisals. So in other words, just because a woman's brain might smell sexy sweat, it doesn't automatically evaluate the source of that sweat (ie, the post-arousal dude) as sexy.