told it was vomit. This fits in with Herz’s theory that our preference for smells is largely dependent on learning and context. On the matter of skunk spray, Herz argues that certain animals, those specifically adapted to a particular habitat, do seem to be born with innate olfactory responses. She argues that humans, as generalists, are different. We’re better off being able to learn quickly whether a smell is bad or good, rather than being preprogrammed to avoid a smell.
Herz suggests that our collective dislike of skunk spray may also be related to the fact that it’s irritating physically. Smells can have feelings associated with them. Menthol feels cool. Ammonia burns. Skunk spray hurts. The feelings associated with smells are picked up by nerve cells in our noses and eyes—these receptors are responsible for the tears we cry over raw onions. Herz suggests that for compounds such as ammonia and thiols in skunk spray, we don’t separate the smell from the sensation. “In actuality, what we’re being repelled by or annoyed by is the irritancy, but we say we don’t like the ‘odor.’”
Skunk spray becomes more threatening in very high doses. There have been reports of dogs dying as a result of being sprayed, according to Wood and Dragoo, although this appears to have more to do with the consistency of the spray than its scent—the oil is thought to coat their lungs. Humans have suffered, too. In 1881, Dr. W. B. Conway, at the Virginia Agricultural and Mechanical College in Blacksburg, recounted a story in the
Whether we are repelled by skunk spray because of its irritancy, because of a cultural construct, or because of an evolutionary predisposition, the annoying quotient doesn’t change much. It’s annoying no matter
It’s not quite clear why we’re able to detect thiols in such low doses. One theory has to do with how the thiols bond with the receptors in our noses. Block says, “There’s no reason why a very low level of a sulfur compound should fit particularly better in an enzyme cavity if you use the old-fashioned lock and key model for enzymes and substrates. There’s no simple explanation for the detection of thiols at extraordinarily low levels, unless you invoke some sort of process where chemically the binding should be extremely good.” One idea is that metals aid in the olfactory binding: “metals, such as copper, do bind with sulfur very, very well,” says Block. “Is it simply a coincidence that a particularly foul-smelling component in skunk spray, 2-quinolinethiol, is also known to strongly bind to metals?” Block asks. Metals in our olfactory receptors could act like glue, helping the molecules attach more securely to the receptors.
There is no question that once those molecules are lodged in a receptor, they’re hard to get out. This leads to olfactory fatigue. The receptors in your nose tire of sending signals. The neurons stop firing, and the brain takes that to mean the odor is gone. This is why tomato juice is thought to work as a skunk spray remedy, says chemist Paul Krebaum. “There’s nothing in tomato juice that takes the smell away. It’s a total myth. What happens to most people—by the time they’re done washing their pets in tomato juice—is that they’ve been exposed to the skunk spray for so long that they’ve developed olfactory fatigue.” Meanwhile, the tomato juice locks into other receptors, causing them to fire. The skunk smell is masked by the tomato smell.
Although tomato juice won’t do the trick, there is something that will. “I was working on a project where we were etching grains of zinc sulfide with acid, and it was producing hydrogen sulfide gas as the by-product,” says Paul Krebaum. It stank. People started to complain. “I needed a way of absorbing this hydrogen waste product as it was being generated.” The solution was a chemical reaction: alkaline hydrogen peroxide transformed those stinky molecules into something else. After his colleague’s cat had a run-in with a skunk, Krebaum wondered whether his remedy might work on the skunk spray, too, because the thiol molecules are shaped like those of hydrogen sulfide. “So I made up a milder version for him,” Krebaum says, and it worked. Recognizing the utility of the discovery, Krebaum wrote to
Here’s how it works: Mix 3 percent hydrogen peroxide with soap and baking soda, apply it to your skunked pet, and rinse. It works by a process called oxidation. The hydrogen peroxide reacts with the thiol to produce a disulfide, which is much less smelly. If the reaction continues, the disulfide turns into sulfonic acid with the addition of more oxygen to the sulfur group of the thiol. Block also uses oxidizing agents for odor elimination in his lab.[1] “We use this in the laboratory because we work with a lot of thiols, and you can’t even flush things down the drain without causing mischief elsewhere in the building because the drains have vents and so forth. You could use peroxide, but bleach is much more effective. Now bleach is not a good remedy for a pet, nor would you want to use concentrated hydrogen peroxide. But a 3 percent concentration is safe.” (Despite the peroxide, Krebaum hasn’t gotten many complaints of fur bleaching.)
Krebaum’s recipe also includes soap, to get the greasy spray off the pet, and baking soda, which he says neutralizes the sulfonic acid and helps convert another stinky component in the spray into something more benign. Thioacetates are thiols with acetic acid attached. “The stinkiest sulfur compounds always have a free hydrogen on the sulfur and some number of carbons on the other side. If you remove that hydrogen and attach acetic acid to it, it’s kind of a temporary attachment because it will break down with water to form a thiol,” Krebaum says. That’s why if a dog gets wet, it will start to stink of skunk again, months after the initial spraying—the thioacetates hydrolyze into thiols, and the smell returns. These chemicals “act to give the skunk spray long-lasting coverage,” says Krebaum. The baking soda raises the pH, which helps speed up the breakdown of thioacetate into acetate and thiols, which can then be oxidized.
This is a rare success story, in which the offending annoyance can be effectively treated. The $3 elixir neutralizes the annoyance on contact, turning it into something benign.
One of our colleagues, NPR science correspondent Christopher Joyce, told us about what annoys him, and he thinks he has it worse than anyone. It’s not that his pet peeve is more unpredictable, longer lasting, or more unpleasant than other people’s. It’s just that he’s annoyed at a time when he should have some respite from being annoyed. He’s annoyed while he sleeps.
You can be annoyed all day long, but you can go to bed at night knowing that except for a noisy neighbor or his dog or a mosquito in the air or a lumpy bed, you’ve escaped the daily mine field of annoyance. Not me.
No, when I go to bed, I enter the annoyed man’s nightmare—the recurring dream. The details change, but the theme is always the same. I’m trying to get somewhere important. I’m trying to catch a plane, and time is running out. Trying to get to a meeting or a class on time. Trying to find a bathroom, urgently, of course. Worst of all, trying to rendezvous with a beautiful woman. Oh, yes, that’s when it’s most annoying.
Because what happens, every time, is that something keeps me from getting there. I’m driving, and I get lost. My cabdriver stops to get lunch and disappears. There’s an accident on the freeway. The public toilets are under repair and out of service. Once there was an earthquake, and I had to get out of a car and walk (I think that was a woman-rendezvous dream).
At first, I struggle diligently to find an alternate route—after all, I’m a responsible person, at least in my dreams. I hail down another cab, book another flight. But soon enough it dawns on me that whatever I do is
