"Occupancy Odor" Affects Emotions

Last Editorial Review: 1/31/2005

Home Scent Home

WebMD Feature

Reviewed By Michael Smith

Remember those cringe-inducing commercials for "house-a-tosis"? Scientists now confirm what some people deny -- houses have signature smells in them and those smells can affect how the residents work and play.

Craig Warren, PhD, visiting scholar at the University of California-San Diego Chemosensory Perception Lab, has logged 30 years in the smell business. He says, "There is definitely something called 'occupancy odor,' which is made up of the unique bodily odors of the residents of a house, plus elements of their lifestyle." Those elements can include pets, smoking, cooking -- and cleaning.

Consider the source, but the makers of the fabric odor remover Febreze recently did a study showing that, on average, Americans don't clean up to 75% of the surfaces in their homes on a regular basis -- the three-quarters that are soft and porous, namely couches, curtains, and pillows. According to the study, odors, such as sizzling fish or frying bacon, may gradually air out and not be as noticeable, but the smell is caught in the cloth subtly, adding to your house's aroma.

Smells Affect Emotions, Emotions Affect Actions

Even if you might not be conscious of it, the smell of your house affects your emotions.

Scientists call this link between smells and emotions the "Proust effect," after the famous novelist who was plunged back into childhood by the scent of a cookie dipped in tea. Smells are processed by the limbic system of the brain. This is an older, primitive part of the brain used to detect danger, fire, poison, or prey.

Smelling begins when the smell molecules enter the nasal cavities and stimulate more than 50 million receptor nerves, which in humans translates to more than 10,000 recognizable scents. Because the smell is recognized in the limbic area, it translates to a feeling or emotion and often to a reaction. "Ewwwww." Or: "Gee, your hair smells terrific."

"A lot of information we have on indoor odors is from Environmental Protection Agency types dealing with indoor air quality," Warren says. "They are mechanical engineers, not chemists." Research called "head space analysis" has been done -- involving sucking in a large quantity of air and then fingerprinting it for the major smell molecules using a gas chromatograph. That can tell you which smell is present, but what is the significance of that?

Instead, Warren and his colleague, Stephen Warrenburg, PhD, associate research fellow at International Flavors & Fragrances, a New York company that creates smells, "mood-mapped" smells. They found that because of the emotional link to smell, people could not describe a smell in words very well, but could tell how it made them feel. The scientists boiled down a list of 44 feelings to eight, positive and negative. The positive feelings were stimulated, happy, relaxed, and sensuous. The negatives were stressed, irritated, depressed, and apathetic.

According to Warrenburg, smells that test "stimulating" and "happy" are usually pleasant to people. "Fruit odors. Zesty odors," he says. "People know what they like and don't like."

So How Should a House Smell?

Warren recommends removing malodors and then testing (sniff) and adding a freshening pleasant smell. "No smell" is detected in mood mapping as unpleasant, he notes. Just covering the odors sunk into upholstery or curtains does not work because the molecules remain after the masking scent has faded. Bad smells require only a few parts per million of molecules and don't wash away, he says, citing mildew as a stubborn example.

This is why Warren was both surprised and happy to learn about the technology of fabric odor removers, which is unique in his experience, he says. "I put this stuff through a torture test," he says. "Tobacco smoke is especially bad because in addition to smell molecules, it has particles." The active ingredient of the products, a starch molecule derived from corn, acts as a molecular sieve allowing the bad-smelling molecules to enter, where they are trapped and rendered incapable of producing an odor.

After foiling the "stinkers," a good, positive smell should be introduced. But what? "Well, what do you like?" Warren replies. This is subjective. Other smells often described as pleasant include citrus and peppermint (more stimulating than happy). Warren is also a fan of a relatively new engineered scent, a flower from Asia, called osmanthus -- fruity and floral, he says. Most people like it, he says.

Peppermint might be a good spritz at homework time. Warren says studies show that the smell lowered the error rate on a boring task, although Warrenburg says the research is thin. Interestingly, smells mood-mapped as "relaxing" as well as "stimulating" also improved performance.

According to Warren, pleasant odors also enhance creativity. Some tests even show that a nice smell can lock a fact into memory and improve recall. Bad smells, on the other hand, are credited with increasing car accidents, family disturbances, psychiatric hospital admission, and 9ll calls.

Much is being done these days with scented candles to change a home's atmosphere,

Warrenburg says. Research also shows people prefer different smells in a living area than a kitchen. Want to put someone "in the mood"? The scent of musk tests as sensuous, Warrenburg confides.

"You feel what you smell first, then think of it," Warren says. What will people "feel" when they walk in your front door? Maybe you think nothing. But studies show that more than three-quarters of people think other people's homes have a distinctive smell, but only 50% think theirs does. Sniff again.

Published Dec. 23, 2002.

SOURCES: Craig Warren, PhD, visiting scholar, University of California-San Diego Chemosensory Perception Lab • Stephen Warrenburg, PhD, associate research fellow, International Flavors & Fragrances, New York.

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