The B.O. wheel

The state of the universe.
March 25 2009 3:20 PM

The B.O. Wheel

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An "aroma wheel" is a popular visual scheme for diagramming the range of smells that characterize a particular food or beverage. A well-known example is the wine aroma wheel, developed in 1984 by University of California-Davis chemist Ann Noble. It is laid out like a dartboard, with broad flavor categories (e.g., "fruity") near the center and specific examples of that category (e.g., "strawberry") on the outer ring. Connoisseurs have built aroma wheels for beer, coffee, brandy, cheese, chocolate, roast beef, and even sewage—but perhaps never for body odor.

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Until now. At the center of the B.O. universe sits its dominant aroma—pure locker-room sweat. From there, the tree branches by gender, reflecting the differences between male and female armpits. Male armpits have more apocrine sweat glands and contain more microbes from the genus Corynebacterium, which manufacture some of the strongest odors. Men also perspire five times as much as women, and their sweat is more sugary.

In January, a Swiss fragrance firm concluded after years of study that female perspiration smells like grapefruit, passion fruit, and onion, while male sweat smells more cheesy, rancid, and animalic. Several years earlier, the same firm had analyzed male sweat and detected these flavor notes: chicken broth, butter, vinegar, onion, and grapefruit. The presence of grapefruit and onion—the scent of a woman—in male sweat gives the lie to the notion that men's B.O. is from Mars while women's is from Venus. For this reason, the B.O. wheel expresses gender differences on a gradient.

Diet also affects body odor. A 2007 study by the Monell Center showed that volatiles derived from turmeric, mint, and garlic can appear in sweat. Other foods whose by-products may be released in B.O. include onion, chili, vinegar, blue cheese, cabbage, radish, fermented milk products, and fish. These foods are condensed into groups on the B.O. wheel.

Other wheel descriptors include "goaty" (named for a gamey secretion of horny male goats) and "boar taint" (the steroid androstenone, also present in boar saliva). These are well-known odorous compounds in armpit sweat. Telephone and e-mail interviews with body- odor and fragrance experts yielded more flavors: wet dog, spicy-cumin, alcohol, and gasoline. To build the B.O. wheel, similar flavors were grouped in accord with existing aroma wheels. The B.O. wheel does not claim to describe all extant body odors.

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