Would you rather smell a sweaty man’s armpit or a sweaty woman’s? Depends on what turns you on. Or off. If you’re into cheesy scents, you’ll find them in a male armpit. But if onion or grapefruit aromas are more your bag, then ask a perspiring lady to raise her arms. Yes, men and women really do have distinctive scents. And thanks to Swiss researchers, we even know which chemicals are responsible for the difference. Both male and females sweat feature 3-hydroxy-3-methylhexanoic acid and 3-methyl-3-sulfanylhexan-1-ol, two names to make you sweat! But they’re not present in equal amounts. The former is the cheesy fragrance that is more abundant in male armpits while the latter oniony smell is dominant in females. Now, here is the interesting part of the story. Neither of these compounds is secreted by the body. They actually form in sweat on the skin from non- odiferous precursors that are secreted. And what causes this reaction? Bacteria! Our skin teems with a variety of bacteria which churn out various enzymes. It is these bacterial enzymes that are responsible for carrying out the reactions that produce the smelly sweat compounds. But different bacteria produce different enzymes and it turns out that for some reason women have more of the bacteria that produce the oniony smell and men have more of the ones that produce the cheesy fragrance. Why this should be so isn’t clear, but maybe it has something to do with hormones creating a more or less hospitable environment for bacterial growth. Deodorants work through anti-bacterial action. Fewer bacteria means fewer bacterial enzymes and less smell. The Swiss study also suggests that deodorant use may be more important for women since an independent panel of sniffers found the sulfurish oniony smell more disturbing than the male cheese fragrance.
There’s another point to consider about armpit aroma. Why does it exist? Is it possible that it actually plays some sort of role in communication? Certainly it is clear that chemical signals exist elsewhere in the animal kingdom. When a female dog is in heat, all the males in the neighbourhood know about it. Can there be some such subconscious signal transmitted through human secretions? Denise Chen at Rice University has gathered some evidence that there may be something to this. She asked twenty heterosexual men to avoid deodorants and other scented products for a few days and then fitted them with little armpit pads while they watched a pornographic video. Electrodes taped to their skin to measure conductivity, a reflection of the amount of sweat produced, confirmed that the men did get aroused. On a separate occasion the men collected sweat produced as they exercised. Chen then recruited young female volunteers to sniff the male underarm productions as their brains underwent an MRI scan. Lo and behold, the scent produced when the men had been turned on activated a different area in the female brain than the exercise induced sweat. What this means is hard to say. Maybe women can subconsciously detect when men are excited. Maybe they can sense when that guy who is trying to look really cool and disinterested is really interested. And of course we don’t really know which compounds in male sweat are being detected. There have been some indications that a steroid, androstadienone, may have a stimulant effect, or it may be the cheesy hexanoic acid. One could test if women are more attracted to men if they have a piece of smelly cheese in their pocket. Oh gee..that was cheesy.