Plain as the nose on your face.

Researchers are breathing new life into our most neglected sense-smell.

A construction company in Tokyo filters a lemon scent into a hotel center to energize visitors in early-morning conferences. In the East London subway, "tea bags" filled with the odor of rose, hyacinth, or apple blossom are activated each time a passenger sits down. American researchers are placing odors in textbooks to see if they'll sharpen reading comprehension and memory.

Sound like a whiff of the future? Think again.

For centuries, the olfactory sense has been relegated to sniffing out hazardous waste or detecting spoiled food. While studies on vision and hearing have flooded the medical journals for years, odor research in the past had been limited mainly to the study of the mating habits of months (pesticide manufacturers have funded more than half the work done on odor signals.)

But all this is changing. In fact, odor researchers, psychologists, and anthropologists have nosed their way into some pretty astounding discoveries about smell. Particular scents are already being used to help insomniacs drift into sleep, keep truck drivers alert, and reduce stress on crowded trains and subways. And that's just the beginning.

Business scents. The Shimizu Construction Company, the world's fifth-largest construction firm, in conjunction with Takasago Corporation of Tokyo, developed the first computerized system to circulate fragrance in enclosed environments, such as homes, offices, high-rise condominiums, hotels, hospitals, nursing homes, and prisons. Company studies found that exposure to lavender, jasmine, and lemon scents triggered a decrease in keypunch errors and a measurable, positive effect on the outcome of corporate meetings.

Other fragrances known for their stimulating or calming effects include peppermint to lessen mental fatigue and the urge to smoke, ocean breeze to ease anxiety, and cinnamon for peacefulness.

Aromachology, the science of fragrance and smell (not to be confused with aromatherapy, which utilizes oils and massage techniques to induce relaxation), is breathing new life into homes, businesses, and health-care facilities across the United States.

Odor research. The National Institutes of Health recently established six clinical research centers for taste and smell disorders.

One of the reasons this "emotional" sense has been overlooked for so long is because it's often quite difficult to study. How do you duplicate odors so that each person sniffs the same thing? What do you call an odor you've never smelled before? How do you turn down the volume of a particular smell?

"We don't understand what it is that is causing the smell or is detected as smell," says Dr. Edward Green, a psychology professor and researcher at the William H. Wheeler Center for Odor Research at the University of Tennessee at Chattanooga. "We know what the stimulus is for vision. We know how much energy has to be there in order for you to see light, what the wavelength characteristics are that you recognize as red or green or purple. We know what enables you to identify a sound as high-pitched or low-pitched, and we know what it takes to make a sound loud or soft. We can't do that with smell."

Smell is learned. Once you're exposed to a scent, you trend to remember it. Unlike the eyes or ears, the nose "never forgets." Some researchers believe this is because the memories of Grandma's apple pie or the smell of gardenias are stored in the lower brain, where there's less interference.

Ever watch a cat sniff the air to see what's for supper or to tell you its litter box needs a good cleaning? When a smell enters its nostrils, receptors immediately send a series of nerve impulses from the olfactory bulb to the brain. In humans the nerves pass through a place in the skull to a part of the brain that is also the seat of emotions. Other senses, like hearing and eyesight, take a longer and less direct route. This may be why smells can evoke such quick, vivid memories. Those recollections may be especially strong when an unexpected smell is encountered or one that hasn't been ] sniffed in a while.

"If you've got a smell that may have been linked to a unique experience, something that you smelled very strongly on a particular occasion, then every time you smell that smell, you're going to remember that occasion," says Green. "Take baked bread, for instance. If only once in your life you were some place and smelled baked bread, when you smell it from then on you'll think, |If only I could go back to Paris and relive the experience I had when I smelled baked bread on the Champs Elysees.' There's nostalgia associated with it. It's a very powerful stimulus for recreating an experience. . . . But I assure you, if you've lived next door to the bakery all your life, you would have no such unique association because everything would be associated with that smell."

Our sense of smell is needed more important than it a first seems. How else would you know when the baby needs changing or when those leftovers pose a threat to your health? Just try to imagine Christmas without the smells of fresh pine. In an odorless world there would be no perfume, no soothing potpourris, no scented candles or soaps. And despite the role of our taste buds, without smell our food would seem very bland and predictable. In fact, except for the four true tastes--sweet, sour, salty, and bitter--the sensation of taste is caused by odorous vapors that rise into the nose. That's why, when you have a bad cold, your meals are about as appetizing as cardboard.

Women are better smellers. During his research Green confirmed what he'd suspected all along--that women are better than men at pinpointing. odors. "Women can identify a citrus or a lemon smell," says green. "They're exposed to it more. Men can do it to a degree, but not to the degree that women can. Men, because of lesser exposure to things like that, tend to characterize smells as being pleasant or unpleasant. If it's pleasant, they label it with a yellow color. If it's unpleasant, they call it purple. Women will get finer shadings.

"The kinds of things that I saw in our associations with color were likely to have been learned by people with a lot of exposure to different foodstuffs. Women identified vanilla. Men didn't. The women recognized cinnamon and coffee and men didn't. Men either liked the smell or they didn't."

Scientists believe that this distinction may lie in hormonal differences, or even in the physiological structure of the brain. Dr. Hilary Schmidt at the Monell Chemical Senses Center in Philadelphia videotaped babies with rattles that either smelled good, smelled bad, or did not smell at all. Schmidt found that the male babies unquestionably preferred the pleasantly scented toys, which female babies played with rattles that were both pleasant and unpleasant. She also found that newborn girls were drawn to odors to which they had been exposed for just a brief period.

Though women tend to be better sniffers than men, about 2 percent of the population has no sense of smell, and others can't detect specific odors. According to a recent report in the New York Times, more than 10 million Americans suffer from chemosensory disorders ranging from a total or partial loss of taste and smell to the perception that a familiar odor smells strange. Researchers believe that most adults are "odor blind" to at least one chemical compound.

Experiments at Duke University Medical Center in Durham, North Carolina, showed that sensitivity to odors begins to decline at around age 60. The older we get, the less we are able to detect odors, distinguish between smells, and tell how strong they are or even what they are.

Of all the illnesses connected with smell, Alzheimer's disease, which afflicts an estimated 2.5 million Americans, has attracted probably the most attention. Studies indicate that people with Alzheimer's show abnormal nerve fibers extending from the top of the nose into a portion of the brain affected by the disease.

Scents and personality. While some are looking for ways to treat diseases like Alzheimer's, others are helping unravel personality quirks. How are select the fragrances we wear, for instance, just may hold the key to who we really are. Extroverts are believed to favor floral scents, while introverts go for heady Oriental aromas.

A study at the College of William and Mary in Virginia showed that people who wear perfume daily perceive of themselves as better than those who don't, are more self-accepting, maintain higher self-esteem and social competence, and are more willing to take a stand on important issues. Men who frequently use cologne see their body images as more appealing than those who don't.

Medical experts are no longer turning up their noses at the mention of odor research. The use of jasmine, peppermint, and patchouli has become more than just a passing fancy, and there's apparently more to this lowly sense than we ever imagined. Nancy Bearden is a free-lance writer living in Chattanooga, Tennessee.