What the Nose Knows: The Science of Scent in Everyday Life (8 page)

T
O THE AVERAGE
person it seems obvious that smoking must dull the sense of smell. Surprisingly, the evidence is equivocal. Some studies find adverse effects of smoking but many, including several recent ones, do not. One, an Australian study of 942 people, found that having a smoke within fifteen minutes of smell testing put a temporary dent in performance. Other than that, “smoking did not reduce olfactory performance or self-assessment of olfactory ability in this group, contrary to previous findings.” The National Geographic Smell Survey reported mixed results. For example, smokers found the artificial musk scent of Galaxolide more intense than did nonsmokers, but the reverse was true for the musky-urinous smell of androstenone. Pleasantness ratings for the skunky-smelling mercaptan sample were higher among smokers, but so were their ratings for rose and cloves. It’s possible that smokers become sensitized to some odors and desensitized to others. In any case, minor effects of smoking observable in clinical testing may have little appreciable impact on everyday smell function. Indeed many perfumers, including the best in the business, have smoked like chimneys.

So strong is the conventional wisdom about the negative effect of smoking that researchers worry when they fail to confirm it. Take the case of a large population-based study in Skövde, Sweden. It linked decreased olfactory performance to several factors including being older, being male, and having nasal polyps. Smoking was not one of the factors. Similarly, diabetes and nasal polyps predicted complete anosmia, but sex and smoking did not. The authors didn’t find that smoking
improved
odor perception; they merely failed to find that smoking harmed it. One can see them bracing for a wave of politically correct indignation when they say, “The lack of a statistically significant relationship between olfactory dysfunction and smoking may be controversial.”

Blind Faith

When, at a party, I own up to being an expert on the sense of smell, I get peppered with questions. (I don’t mind this—if I’m not in the mood for Q&A, I tell people I’m “in the chemical business” and the conversation grinds to a halt.) People often ask about smell ability. Who is better: men or women? perfumers or normal people? Curiously, one comparison doesn’t come as a question but as an assertion. Wineglass in hand, someone will inform me in earnest tones that “blind people have a heightened sense of smell.” Others confidently assure me that “Helen Keller had an incredibly sensitive nose.”

Helen Keller has been dead since 1968, but remains a powerful symbol of the belief that blindness turns people into super-smellers by way of compensation. (The Marvel Comics hero Daredevil embodies the same idea.) Despite her iconic status, Helen Keller herself did not claim to have a supersensitive nose. In her famous essay “Smell, the Fallen Angel” she describes what she is able to smell. Amid lyrical, somewhat overripe prose (“Smell is a potent wizard that transports us across a thousand miles and all the years we have lived”), she gives specific examples of her olfactory ability. Let’s compare her talents to ours. Smells trigger memories—check. Approaching rainstorms have a smell—check. Can smell if a house is old-fashioned and long-lived-in—check. Can smell a person’s occupation (painter, carpenter, ironworker)—check. Close friends have distinctive odors—check. Babies smell sweet—check. Nothing extraordinary so far. Helen Keller does not sound like a nasal genius. Indeed, nowhere does she claim to have a more sensitive nose as a result of being blind, or that her sense of smell is better than that of sighted people. On the contrary, she writes, “I have not, indeed, the all-knowing scent of the hound or the wild animal.” She also says, “In my experience smell is most important.” It is not surprising that, being blind and deaf, she finds smell to be her primary way of sensing the world.

Helen Keller’s modest assessment of her own ability has done little to dampen enthusiasm for the idea of smell compensation in the blind. It seems so reasonable it must surely be correct. But is it? There is plenty of experimental evidence that addresses the question—in the last twenty years, six studies have compared smell in the blind and the sighted. Without exception, they find that the blind are no more sensitive than the sighted—both groups detect odors at about the same concentration. Nor do blind and sighted people differ in the ability to discriminate one odor from another. Even the brain waves triggered by odor stimulation are similar in blind and sighted people.

Blind people may have one advantage: in three of the six studies, they were better at naming odors. Even here, their success depended on cognitive factors such as memory rather than hyperacute perception. Based on her own words, and on what has been observed in experiments, Helen Keller’s ability to navigate the smellscape was not the result of a supersensitive nose. Rather, it was a triumph of the adaptable human brain making the most out of a perfectly ordinary nose.

The Nose on Freud’s Face

Sigmund Freud was not a big fan of the nose. He believed odor perception was vestigial, the sensory equivalent of the appendix. In his view, smell became obsolete when our evolutionary ancestors took on upright, bipedal posture and put distance between the nose and the ground. At the same time, Freud’s ape-man discovered shame and disgust in the exposure of his genitals. This led him to turn away from the stink of excrement and to suppress his sense of smell in general. To Freud, this was a vital precondition for the emergence of civilization—the repression of smell meant the repression of wild sexual impulses and their redirection to more refined behavior. Freud thought that children recapitulated the history of the species as they grew up, and thus that the infant’s early interest in smell fell away like embryonic gill slits. Freud’s leading American disciple, A. A. Brill, summarized the master’s view: “All children make good use of the sense of smell in early life; some of them, as we shall learn later, retain it even in adult life; most of them, however, lose it, so to speak, as they grow older.” To the orthodox analyst, psychologically mature adults move on and leave fascination with smells to perverts and neurotics.

Like many of Freud’s theories, his views on smell are difficult to summarize without making them sound simpleminded and ridiculous. The original texts consist entirely of a few sentences in a letter to his confidant Wilhelm Fliess, a German ear-nose-and-throat physician, and two footnotes in the book
Civilization and Its Discontents
, and are part of what historian Peter Gay called Freud’s “audacious, highly speculative venture into psychoanalytic prehistory.” Nevertheless, after becoming part of the bedrock of psychoanalytic theory, they helped devalue smell in the wider intellectual world.

It is puzzling that Freud, who found a sexual angle in every other facet of psychology, thought it had so little to do with the sense of smell. Is sexual attraction no longer an affair of the nose? Are modern women scentless and modern men oblivious, or vice versa? In a recent University of Texas study, men said T-shirts worn by women near the time of ovulation smelled more pleasant and sexy than T-shirts worn during a nonovulatory part of the cycle. Modern women, it seems, continue to produce a scent cue associated with ovulation and modern men continue to respond to it. This low-technology experiment could have been done in Vienna in 1930 or New York in 1932, had either Freud or Brill cared to test their theories.

Brill toed the party line when he wrote in 1932 that “the sense of smell unlike the sense of sight plays a very small part in the life of civilized man,” and “modern man has little need of his sense of smell.” Though surrounded by modern, civilized men, Freud and Brill never bothered to ask their opinion. The psychologist Paul Rozin and colleagues got around to it a few years ago. They asked people to rank the unacceptability of permanent loss of sense of smell, loss of hearing in one ear, and loss of the left small toe. According to about half the respondents, loss of smell was the least acceptable alternative. The average person is not as dismissive about the sense of smell as Freud thought he was. What could have motivated Freud to construct a psychoanalytic conjecture so flimsy it could be blown up with a simple opinion poll?

The experts think it was something, well, Freudian. The psychoanalyst Annick Le Guérer attributes it to Freud’s “repression” of his “transferential relationship with Fliess.” The anthropologist David Howes thinks Freud’s conflicted emotions toward Fliess led to his “denial of nasality” and a desire to “cut the nose out of psychoanalytic theory.”

I have a more straightforward hypothesis. Based on the facts of his medical history, I suspect Freud suffered from hyposmia. The repeated insults of cocaine, nose surgery, influenza, sinus infection, cigar smoking, and finally aging left him with a clinically impaired sense of smell.

Freud caught influenza in the spring of 1889, at the age of thirty-three. The infection was severe enough to leave him with a persistent cardiac arrhythmia, so it could easily have affected his nose. In his letters to Fliess from 1893 to 1900, Freud often complains of nasal congestion with discharge of pus and scabs, both symptoms of sinus and nasal passage infection. Freud suffered from migraine headaches, which he treated with nasal applications of cocaine prescribed to him by Fliess. Fliess operated on Freud’s nose twice to remove and cauterize part of the turbinate bones. On top of all this, Freud smoked heavily; his typical rate in the 1890s was twenty cigars a day.

Freud’s nose was already a medical disaster zone when he hatched his smell theory in 1897, and my hunch is that he was already smell-impaired. When he wrote
Civilization and Its Discontents
in 1930, he was seventy-four years old and suffering from cancer of the jaw as well. In my view, Freud’s intellectual indifference to smells was the result of sensory deprivation—the gradual onset in adulthood of severe hyposmia. His ludicrous idea that smell was active in children but ceased to matter for adults had nothing to do with his feelings about Wilhelm Fliess. It was simply an overgeneralization of his unfortunate personal experience.

Our Rank in the Animal Kingdom

No doubt there is a vast difference in power in the sense of smell in both these animals [deer and dog] and in man; nevertheless, I do not think so meanly of man’s olfactories as some physiologists appear to do.

—W. H. H
UDSON,
On the Sense of Smell
(1922)

After finishing my PhD at the University of Pennsylvania, I began working a few blocks away, at the Monell Chemical Senses Center. I received a fellowship to study there with Dr. Kunio Yamazaki. He had several lines of inbred mice used for cancer research; the lines were genetically identical except for a set of genes known as the Major Histocompatibility Complex (or MHC), which controls the body’s tissue-rejection response. They are the genes used to find whether a person is a suitable match as an organ donor. Yamazaki’s mice preferred to mate with individuals bearing a different MHC type apparently on the basis of smell. My plan was to study the behavior behind the odor-based mate choice using competitive mating experiments, where the female had access to multiple males of different MHC types.

Watching the mice choose mates, I became curious. Could humans detect the odor differences that were so apparent to the mice? Soon I was running my first experiment on human odor perception. I had blindfolded people sniff live mice in Tupperware containers with holes cut in the sides. Occasionally a mouse tail would get up someone’s nose; this seemed to bother some people more than others. The judges also sniffed tiny test tubes filled with mouse urine or dried fecal pellets. (Thankfully, no one inhaled a mouse turd.) For every odor source the results were clear: untrained humans could distinguish between the mouse strains based on smell alone. The uncanny scent powers of mice were well within human reach. I wrote up the results as a man-bites-dog story for the
Journal of Comparative Psychology,
and it eventually became one of the mostcited scientific papers I have ever published. By encouraging me to continue exploring human odor perception, it also led to my career in the perfume industry.

Deborah Wells and Peter Hepper discovered an even more impressive man-smells-dog story. They had dog owners sniff two identical blankets, of which one had been slept on by their pet and the other by an unfamiliar dog. The owners correctly identified their dog 89 percent of the time. The strength or pleasantness of the smell was not a factor, nor were non-doggy household odors.

Stories about the amazing ability of the canine nose highlight the dog’s talent and ignore how the feat is stage-managed by humans. (“Pay no attention to that man behind the curtain!”) Consider the recent finding that dogs can sniff out bladder cancer. The dogs in question were trained exhaustively with human urine samples. Training began with search-and-find games and progressed to more complex tests. Urine samples were carefully selected so the dogs would learn to ignore irrelevant dietary odors. The trainers also counterbalanced samples from smokers and nonsmokers, patients and healthy people. After seven months of training, the dogs were ready for the decisive test: to pick the single positive sample from a set of seven. As a group they were correct 41 percent of the time, which successfully beat the random odds (which were one in seven, or 14 percent). The resulting scientific report made headlines around the world.

So, yes, dogs can smell odors associated with bladder cancer. But this is a far cry from “What’s that, Lassie? Timmy has bladder cancer?” To make use of this canine talent, your local hospital would have to maintain a half-dozen dogs and their trainers, supply copious medically certified human urine samples, and provide ongoing statistical support and chemical analysis. At which point six out of ten bladder cancers would go undetected.

If the human nose received the same gee-whiz treatment given to animal stories, we would sound as impressive as any dog. Here’s an example: Just by smelling some ice cream that once had a wooden popsicle stick in it, regular folks can tell whether the stick came from Wisconsin, Maine, British Columbia, or China. Amazing, no? How do those monkey-people do it? In this case, wooden sticks from each locality were frozen in vanilla ice cream for six days. The samples were melted and the sticks removed. The sniffing primates—Ohio State graduate students—had to pick the same sample from a repeatedly presented pair of samples five times in a row to be declared a success. All possible pairs of wood source were tested. Two judges failed—they couldn’t tell one stick-scented ice cream from another. Eight judges succeeded—they could reliably discriminate anywhere from five to nine of the ten possible pairings. Not bad for humans. Could the judges explain how they did it? Unfortunately not, but then, neither could the cancer-sniffing dogs.