Our bodies speak to one another in airborne chemical signals that bypass our conscious brains. In BLONDES I fixate on this truth, detailing studies that have shown exactly how these chemicals, called sex pheromones, can trigger sexual attraction. Some studies show that sex pheromones have a marked effect on behavior — potentially making women more receptive, upbeat, and attracted (in the case of androstadienone-related odors) and men more drawn to the body odors of a woman when she’s most likely to conceive (in the case of estrogen-related odors).

And now a news flash: sex pheromones aren’t the only types of pheromones that may affect human behavior. There are also alarm pheromones – chemical signals, like fear gas, that make a person more alert, more on edge. Stony Brook University neurobiologist Lilianne Mujica-Parodi and her colleagues taped absorbent pads into the armpits of 144 first-time skydivers, collecting their fear sweat before and during a 13,000-foot free-fall jump. Then the research team enlisted another set of volunteers to smell either a.) the skydivers’ sweaty pads (fear sweat); or b.) pads worn by sweaty subjects who had simply been working out (exercise sweat), while having their brains scanned by fMRI. Although participants rated fear sweat and exercise sweat as having a similar intensity, their brains responded to the two sets of sweats in dramatically different ways. It turned out that fear sweat — and only fear sweat — triggered activity in the left amygdala, the region of the brain associated with fear. When shown pictures of faces with expressions that ranged from happy to furious, and asked to identify the emotion, people exposed to fear sweat were more accurate when distinguishing between angry and neutral expressions. A chemical component of the sweat, it appears, put them on their guard. The researchers call it “second-hand stress.”

None of this is surprising to biologists because other animals, even mammals, use alarm pheromones all the time. After inhaling alarm pheromones, rats and deer sniff and pace around, unable to let down their guard.

I’m intrigued by this. Alarm pheromones are a hidden biological component of our survival as social anim

als. Anywhere people are stressed or scared — exam rooms, hospitals, interrogation chambers, battlefields, trading floors, sports matches — there’s a residue in the air. Call it an ambient emotion. Call it emotional infection. Call it evolutionary hardwiring that primes us to act when there’s danger. Are some of us more sensitive to it than others? Probably. And its effect on behavior is no doubt context-dependent. I’d like to see more studies, a bigger n, and more distinction between genders.

Like many writer types, I’m hyper-sensitive to the emotions of others, sometimes to the detriment of my psychological well-being. If you’re scared, I worry. My guard goes up, too. Block my my olfactory system, the odor processing region where alarm pheromones may be processed — and would I be less sensitive to your stress?