Aroma Therapy / In The Military, It's Known As 'Nonlethal Weapons Development'

A lot of work goes into smell these days -- and because of that, we've evolved into quite a minty-breathed species: soaped, deodorized, conditioned, roaming the world in T-shirts that smell like an ocean breeze.

As a rule, far less effort has been put into enhancing bad odors over the years. Few people, understandably, have dedicated their lives to amplifying the reek of rotting meat or stored sewage. As it happens, however, this is exactly what cognitive psychologist Pam Dalton at the Monell Chemical Senses Center in Philadelphia does. And all in the name of national security.

Dalton's malodor work is funded in large part by the Department of Defense, and is part of the burgeoning field known as "nonlethal weapons development." The Army, the CIA, local law enforcement -- everybody these days wants to develop the next-generation stink bomb. "For crowd control, warfare applications, to discourage people from hanging around certain facilities," Dalton says. "Goodness knows, it's clear that odor deterrence works! You wouldn't lean against a dumpster and hang out."

Unbeknownst to most of us, odors have a long history of being used as deterrents by the government. During the Christmas season county administrators in the northeastern United States will sometimes spray public-property evergreens with a fox-urine-based repellant, in order to discourage poachers. In subzero weather, and open air, the scent is barely detectable. But bring the tree into a closed, 70-degree house and it'll stink up the place. (Posted signs warn would-be tree thieves about the spraying.)

The real roots of Dalton's work go back to World War II -- to a compound called Who Me that was designed for use by the French Resistance. Who Me smelled like fecal matter, according to Dalton, and was issued in pocket atomizers. The plan was for a Resistance member to sidle up close to one of the German officers then occupying Paris and unobtrusively spray him.

"This, of course, would totally embarrass the officer," Dalton explains straight-faced. "And Germany would then lose the war." The flaw in the plan -- or perhaps, one of the flaws in the plan -- was that Who Me's ingredients were extremely volatile and therefore hard to control: The person who does the spraying ends up smelling as bad as the sprayee. For two weeks, Paris reeked. Afterward, "The experiment was pretty much deemed a failure," Dalton says.

Since those heady days, stink bombs have gone through various stages of being mothballed and resurrected by the military. Back in the 1970s, Dalton recalls, the Army drained chicken eggs, filled them with rancid-smelling chemicals, and then tested the effects by lobbing them at enlisted men. "The project never really took on a life of its own," Dalton sighs.

As the '90s rolled around, however, the definition of "necessary force" grew narrower; nonlethal weapons programs bloomed, producing acoustic dazzler grenades that flashed blindingly bright lights, and a slippery foam that could be sprayed on the streets to keep people from walking or driving. Always in the back of the military's mind, however, was smell.

But coming up with useful applications of stink turned out to be difficult. For starters, there was the problem of acclimatization: After 15 minutes of immersion in an odor, most people become unable to smell it -- which means that an odor's usefulness as a trespassing deterrent was limited. (The olfactory system is designed to detect changes -- the way our visual system might detect motion -- rather than constantly perceiving the smell landscape.) Another problem that bothered the military was universality. How do we know that "bad" odors will be the same around the world?

As it turns out, we don't. Unlike food tastes, the way we react to an odor is largely learned. "There's no evidence that babies from birth naturally prefer one smell over another," Dalton notes, "although they do prefer certain tastes."

In the past, marketers had looked into which good odors crossed cultures, and discovered that the smell that signifies "clean" in South America was not the same as a "clean" smell in Asia. Dalton and her colleagues now wanted to find the smells that nobody anywhere liked: smells that universally, unambiguously stink.

The group chose to test mostly biologically based odors, on the theory that they were more likely to have deeply rooted aversive powers. "Sweat, vomit, feces, we tested all of them," Dalton says. "And sulfur, which is the smell of decomposition and decay and which might therefore be aversive" -- a sign that your food, or your friend, is rotting. Dalton even visited a barber and brought back a huge bag of human hair, which she burned -- though not with any spectacularly aversive results.

After months of trials, the winners of Dalton's most noxious odor contest turned out to be -- surprisingly -- good old Who Me, along with a scent known in the trade as U.S. Government Bathroom Malodor (the standard reek against which commercial companies test their bathroom air fresheners).

But while these two odors topped the list for general unpleasantness, Dalton and her associates also discovered that people's reactions to odors varied dramatically, depending on the situation in which the scent was smelled. (In normal tests, for instance, people like the smell of wintergreen. But in situations where subjects are told that they'll be smelling an industrial solvent -- but are still given wintergreen -- they won't like it. Most, in fact, will feel actually sick.)

In an age of biological and chemical warfare, these psychosomatic odor effects may make stink weaponry more effective than ever -- and explain the military's renewed interest. As Dalton observes, to smell something unfamiliar in a lab after signing a consent form is one thing; to smell something unfamiliar in a war is far more unnerving.

(Exactly how unnerving, Dalton and her colleagues have even quantified: Subjects given a proofreading test made more mistakes when assaulted by a mystery smell, and were sometimes so addled that they reported concentration problems even after the test was officially over.)

So far, according to Dalton, none of the new research on odor warfare has yet reached the development stage. When it does, the military will presumably go back to testing hollowed-out chicken eggs, or more advanced mechanisms of delivery. This may take awhile, though. In the meantime, it's probably not worth holding your breath.