How the Nose Knows

Sunday, October 28, 2007


Discovery Our Enigmatic Sense of Smell

By Rachel Herz

William Morrow. 266 pp. $24.95

Nineteenth-century French food writer Brillat-Savarin said almost 200 years ago that "but for the odor which is felt in the back of the mouth, the sensation of taste would be but obtuse and imperfect."

In The Scent of Desire, Rachel Herz goes way beyond "obtuse and imperfect." She writes that without the sense of smell, there would be no sense of taste at all. That smell and taste are conjoined is just the beginning; smell is linked to everything from memory to sex. Smell is deeply linked to our emotions; both are processed in the same area of our brains, and aroma triggers emotions even more strongly than can any of our other senses. Those who suffer from anosmia or "smell blindness" are devasted by their condition.

By the same token, smell is a memory trigger. Herz cites Proust's madeleine -- the small cookie that spawned a masterpiece. Proust wrote about the taste of the madeleine and its accompanying sip of tea: "No sooner had the warm liquid . . . touched my palate than a shudder ran through my whole body." But Herz says the smell is really what did it. The nose processes aroma in two ways: from the outside, and from inside the mouth, at the back of the palate. Without the scent of the madeleine, there would have been no taste -- and no Remembrance of Things Past.

Even sex would be diminished without the sense of smell. It's not perfume and aftershave that get us -- it's the way we ourselves smell. Just as animals sniff to check each other out, most of us recognize body smell without being aware of the process. Our own cheek-to-cheek social kiss may be a remnant of the sniff greeting. Herz explains the genetic coding of our immune systems, called the major histocompatibility complex (MHC), which is externally manifested by body odor. Since each person's MHC genes are unique, like a fingerprint, body odor is also one of a kind. We are attracted to mates whose MHC differs most from our own, offering us the best range of genes for our mutual offspring, should that good fortune come to pass.

In a classic experiment, men slept in cotton T-shirts for two nights; the lucky women in the experiment got to smell the T-shirts and then rated them for sexiness and pleasantness. The women consistently ranked shirts from men whose genes differed most from their own as the best. Thus -- without being aware of it -- do we choose our mates. (All else being equal, one presumes.)

There's much more here that's fascinating: Humans have 20 million olfactory receptors in our noses (more receptors than in any other sensory system except vision), while dogs have approximately 220 million; electronic noses are also better at smelling than we are; smells are perceived differently in different cultures; as we age, some of us lose the sense of smell; newborn babies and their mothers recognize each other by their body smells.

Unfortunately, a great deal of Herz's writing is academic at best and clunky at worst. Consider this sentence: "Olfactory-emotion translation proposes that the sense of smell and emotional experience are fundamentally interconnected, bidirectionally communicative and functionally the same." That needs to be read several times, and it's still not totally clear. Then there's this: "Craving is 'an intense desire to eat a particular food,' says Marcia Pelchat. . . . The key words are intense desire and particular food." That doesn't leave much.

But this is a serious book, with many whiffs of delight, even if the title is a little deceiving: The Scent of Desire is about a lot more than those smelly T-shirts.

-- Bunny Crumpacker is the author of "The Sex Life of Food" and most recently "Perfect Figures."

© 2007 The Washington Post Company