Alan Hirsch has a vision of the future. You can't see the vision. But you can smell it: "Ten minutes before you wake up, your alarm clock will release a puff of a wake-up smell," said Hirsch, a neurologist, psychiatrist and maverick scientist of smell. "At work there will be odors to reduce the chances of errors. After work, an odor to relax. At the gym, an odor to increase exercise strength. And later an odor to eat more or less."

In the evening, said Hirsch, sitting at a solid marble desk in the plush headquarters of his Taste and Smell Research Foundation in Chicago, "there will be an odor to make you more amorous." And then, he said, "one to help you sleep better."

Hirsch is one of a growing number of doctors, psychologists and molecular biologists turning their attention to the sense of smell. Their target is elusive; of all the body's senses, smell is probably the most difficult to study and the least well understood. Yet it may be the most broadly influential, affecting our moods, memories, problem-solving abilities -- not to mention our sexual appetites and choices of mates.

"The field of smell is an enormous untapped field, especially for how it affects people's behaviors and emotions," Hirsch said. "There's an entire universe at the tip of your nose and we know so little about it."

That's starting to change. This spring, Hirsch reported results of a study indicating that men are sexually aroused by the combined smell of lavender and pumpkin pie much more than they are by traditional perfume fragrances. Other recent work by Hirsch has suggested that certain smells can speed learning, improve memory, help in weight loss, affect aggression levels and even alter one's sense of how big a room is.

Hirsch's findings remain preliminary and are rejected by some experts as oversimplified. But other studies too have begun to hint that odors may have a pervasive, if largely ignored, influence on day-to-day life. And while some may balk at Hirsch's heavily scented future -- fearful that we will become a population of odor addicts overbeholden to our no\s\es -- experts argue that since odors are ubiquitous anyway, we might as well pick and choose them to suit our needs.

"Smells are always present," Hirsch said. "The question is, do we want to just leave it up to what the last carpet cleaner was? Or do we want to take some control over what we smell? Even unscented soap is scented to smell unscented." On the Scent of Understanding

The intimate linkage between odors and emotions is mostly a matter of biological wiring. Vision, hearing, taste and touch send their sensory input to the front of the brain, where logic and cognition can rationally interpret the information. By contrast, smell has a direct line to the limbic system, the primitive "reptilian" part of the brain that generates our most basic emotions: fear, rage, affection, lust.

Of course, people have known for a long time that scents -- whether made by glands in the body or by scientists at Chanel -- can have a powerful influence on feelings and behavior. Perfumes have been around for centuries. And Freud hypothesized that human civilization could never have developed had we hairless apes not gradually lost our animal olfactory sensitivity, freeing us from the otherwise unavoidable obsession with the smells of sex and violence in the air.

Yet only in the past few years have scientists moved beyond old-fashioned studies that simply looked at how people responded to certain smells and started to explore the biological and neurological nature of smell. Just two years ago, for example, scientists at Columbia University identified the family of genes that allow a postage-stamp-sized patch of tissue within the nose to sort through the approximately 10,000 different smells that humans can perceive.

"Fragrance research can be a sort of froufrou discipline on its own," said Avery Gilbert, a biopsychologist and president of Synesthetics, an odor consulting company in Montclair, N.J. Just look at the many "aromatherapy" products that now fill the shelves of health food stores, he said, few of which have been validated with any real scientific rigor. "Now we're coming out of the dark ages with smell. We are really getting a better grip on how smell works in our daily lives. And soon what we'll really be able to do is design fragrances for very specific effects." A Cucumber for Claustrophobia?

Hirsch's recent study of smells that are sexually arousing to men, in which he tested 30 different scents just to see if anything worked, is a classic example of the old shotgun approach to smell research -- an approach that some criticize as "cowboy science" but that Hirsch says can at least help identify smells worth pursuing further. Using a device resembling a miniature blood pressure cuff that measured blood flow in the penis, he and his team of nurses documented penile blood flow changes in 31 men while the men breathed through differently scented surgical masks.

Charlene Bermele, a registered nurse who worked on the project, speculated on the results, saying, "I don't know if it was the odor itself or something about us."

Whatever the test was really measuring, the results were hardly classically romantic: A combination of lavender and pumpkin pie increased penile blood flow the most, by about 40 percent, and the combined smells of doughnut and black licorice scored second, with an increase of more than 30 percent.

"You'd expect chocolate to be high, with St. Valentine's day and all, or flowers at least," Hirsch said. "But chocolate increased blood flow less than 3 percent. Rose increased it only 3 1/2 percent." Even pizza did better than that, Hirsch said -- although, he added, given the Windy City's well-known penchant for pizza, "that finding could be something unique to Chicagoans."

In another study, Hirsch looked for a scent that could shorten the time it takes to learn how to solve a maze-like puzzle. In keeping with his shotgun approach, he tried all kinds of smells with all kinds of rationales. He tried lavender because that odor can increase alpha waves in the brain, a sign of relaxation, which might enhance learning. He tried jasmine because that scent can increase beta waves, which are a sign of being awake and alert. He tried the smell of baked goods, thinking the comforting aroma might put people in a positive mood and make them more attentive. He even tried the smell of grapefruit, based on his personal experience that a glass of grapefruit juice in the morning seemed to jump-start his day.

None of those scents worked. But for reasons unknown, a mixed floral smell did. People sniffing the floral bouquet improved 31 percent between their first and third attempts to solve the puzzle, as compared to a 14 percent improvement in people who wore masks with no scent.

In yet another study, involving thousands of participants, Hirsch gave odor-charged "pens" resembling capped, felt-tipped markers to adults wishing to lose weight. Whenever you have an urge to eat, he told them, remove the cap and briefly sniff the smell. (Earlier he had tried a similar approach with medical students and Hershey bars, to see if an occasional sniff of chocolate might suppress appetite. But at the end of the day all the bars were gone. "The lesson," Hirsch said: "Don't trust medical students with Hershey bars.")

Six months into the sniff-pen study, which included several different smells generally perceived as "pleasant," participants had lost an average of about five pounds, with the more frequent sniffers (some sniffed more than 200 times a day) losing the most. It's still not clear, Hirsch said, whether the smell itself suppresses appetite or whether the act of sniffing simply reminds people not to go for the potato chips.

Then there was the work with claustrophobia. "We'd been doing group therapy with people with smell loss," a common complication of head injury, Hirsch said. "And a lot of people were saying, Since I lost my sense of smell, I can't stand riding in an elevator anymore.' " Might smell have something to do with space perception?

To find out, Hirsch created a human-sized plastic tube, resembling a cylindrical phone booth or the orgasmatron in the Woody Allen movie "Sleeper." He had people stand inside the tube while he infused different odors and then had them fill out questionnaires to test their sense of space. The results: The smell of green apples or cucumbers caused the space to be perceived as larger than it was. Barbecue smell made it seem smaller.

"Something like 10 percent of the population is claustrophobic," Hirsch said. "If you can just take out a cucumber and smell it or bite it, that might be a simple solution. Or if you have a small room, you could use this smell to create the illusion of a bigger space."

Hirsch also foresees using space-expanding smells in airplanes or magnetic resonance imaging machines -- medical diagnostic chambers that are so confining as to make some patients panic before their test is finished. And who knows? Hirsch said, maybe agoraphobes, people with a fear of wide open spaces, might want to carry around a bottle of barbecue sauce. Early Impressions

While Hirsch's work is provocative and has helped get the human nose into the public eye, his studies are mostly small and many researchers suspect they overstate the effects of particular smells. Smell is not like taste, experts note, in which bitter flavors are rejected by almost everyone (probably because they warn of poison) and sweet ones are universally liked (sugar being a valuable energy source). Rather, preferences for certain smells -- and many of the personal effects of those smells on mood or behavior -- vary considerably among individuals, probably as a result of positive or negative experiences that different people associate with those smells from early in life.

Research has clearly shown that smells make strong impressions from the first days of life. Within a week after birth, for example, infants offered two identical pieces of clothing show a clear preference for the one that has been worn by their mother, turning their head in the direction of the cloth and stretching toward it. Similarly, by smell alone mothers can distinguish between a T-shirt worn by their child and one worn by another.

Moreover, those recognition patterns may last forever. Michael Leon, a neuroscientist at the University of California at Irvine, has shown that in infant rats, at least, the part of the brain that responds to smell undergoes subtle but permanent structural changes during that early period of mother recognition, as though the smell pattern were getting "hard-wired" into neurological memory. The same thing happens when an artificial smell is substituted for the mother, if that smell is accompanied by physical contact similar to what a mother would provide. And whether it is the mother's smell or an artificial perfume that these newborns sniff during the first few days, their fondness for that smell never goes away. Given a choice of odors later as adults, Leon said, they will gravitate toward that smell in preference to all others. Most will choose a mate with a similar smell, though whether that's true in humans remains unknown.

Perhaps because of such personal differences, most attempts to use specific smells to enhance mental performance or accomplish other specific tasks have fallen flat, said Susan Knasko, an environmental psychologist at the Monell Chemical Senses Center in Philadelphia. Of the dozen or so truly rigorous studies in which people were exposed to various smells during a word construction test, she said -- such as being asked to create as many words as possible from a group of letters -- most smells showed no consistent effect at all.

"Individuals differ," said Charles J. Wysocki, a neuroscientist at Monell. "People have their own baggage that they carry into these experiments, and experimenters are often unwary of that baggage. We have to be careful about making willy-nilly claims without the data to back it up."

But while it may be difficult to find a smell that everyone responds to in the same way, individuals can use fragrances for their own specific purposes. Research by Rachel Herz, a cognitive neuroscientist at Monell, has shown that when people are asked to memorize a list of words and they do so in the presence of a distinctive odor -- almost any odor -- they'll be able to remember more of those words a couple of days later if, when they are tested, they are given a sniff of the same odor. The technique takes advantage of fragrances' well-known ability to stir up remembrances of things past -- a phenomenon made famous by the French novelist Marcel Proust, whose childhood memories were so vividly evoked one day by the taste and smell of a tea-soaked pastry.

Herz said the smell-related recall technique works even better when the first "learning sniffs" occur in an intense emotional state, such as high anxiety about the upcoming test. The work suggests that students might benefit from studying under the influence of a fragrance and then wearing that same fragrance when they take their test -- although a separate fragrance might be needed for each subject, to avoid confusion.

"If you study with an odor only associated with your economics course, and then wear that cologne when you go in for your economics test, it may help," she said.

Moreover, it may be worth doing some personal experimenting with bath oils, soaps or perfumes to see if a certain scent relaxes or cheers you up, since studies have clearly documented that odors can affect mood, said Susan S. Schiffman, a professor of medical psychology at Duke University. In research using widely accepted measures of psychological states, Schiffman has shown that pleasant odors such as some floral scents can significantly improve people's moods. And in a landmark study on the effects of bad smells, she showed that much of the crankiness afflicting residents of a small North Carolina community could be attributed to a stinky 80,000-pig farm at the edge of town. Cinnamon Fire Alarm

It's one thing to prove that having 80,000 pigs for neighbors can mess up your mood, and another to prove that certain scents can precisely tweak your appetite, mental acuity or libido. Yet researchers said that a new generation of scientific tools is helping them close that knowledge gap. They're hoping that a closer look at the molecular biology of smell will show that some odors affect most people in similar ways, a finding that would open the door to the rational engineering of our odor environment according to the rules of a new science that Gilbert calls "the ergonomics of smell."

Already, molecular biologists are sifting through the recently discovered odor receptor genes to learn exactly how the nose responds to smell. And using functional magnetic resonance, a new medical imaging technique that creates a detailed motion picture of brain activity, scientists are seeing how various brain regions react when they apply tiny droplets of chemical scents to patches of the nose's interior.

Who knows what's possible? In one striking set of experiments, Schiffman recently found that by spiking foods with aroma enhancers she could strengthen the immune systems of elderly people who ate the food. In another study of 25 sleeping people, she showed that a fire alarm that releases a stimulating Chinese cinnamon scent may be an effective alternative to traditional alarms for the hearing impaired, waking up three-quarters of the people in less than a minute and a half.

In the future, Gilbert said, "people will know what they're doing when they use smells. It will be much more customized, allowing consumers to select a range of products that augments their mood in a specific direction."

That prospect inevitably gives rise to the question of whether such mood manipulations will be acceptable, or whether they will be seen as a form of drug use. After all, if one substitutes the word "pill" for the word "odor" in Hirsch's description of the future -- one pill to wake up, another to stay alert, another for good sex and yet another to go to sleep -- the future starts to look like one big chemical cocktail party.

The Food and Drug Administration defines a drug as a substance that is "intended to affect the structure or the function of the body." And while the agency has not waded into the aromatherapy field, said FDA spokeswoman Ivy Kupec, that's at least partly because no specific health claims have yet been made. The more specific the claims get, the more likely it is that the agency will wake up and smell the regulatory coffee.

"It's a fine line that the fragrance industry is walking now," said Monell's Wysocki. "I'm certain no fragrance company wants to have FDA oversight. They'd have to go through double-blind drug trials, which cost millions of dollars and go on for many years. That's not at all what they are looking for."

Most scientists seem unworried about that prospect. "If you show that smells have physiological effects, then someone may say that makes them a drug," said Gary Beauchamp, Monell's director. "But when you're thirsty, a glass of water has physiological effects, and I don't think that makes it a drug."

Hirsch agrees, comparing the future use of odors to the use of Muzak today -- just an everyday part of our mood environment. "It will always be a balancing act of who will be helped and who may be harmed," he said. "But there is a tremendous potential to help. Perhaps we can find an odor that will make peace."

World peace probably won't come that easily. But if nothing else, Hirsch said, perhaps that next root canal can be more pleasant. "Everybody recognizes and dislikes the smell of a dentist's office. They could use some help." CAPTION: HOW THE NOSE KNOWS The human nose can detect about 10,000 different smells. The sense of smell accounts for about 90 percent of what we think we taste. Hold your nose and you won't be able to tell the difference between a bite of apple and a bite of onion. An odor molecule inhaled through the nose gets warmed and moistened on its way to the upper reaches of the nasal cavity. There is hits a patch of tissue about the size of a small postage stamp, the olfactory epithelium, rich with nerve cells bearing specialized receptors. The receptors send signals to the adjoining olfactory bulb, an extension of the brain, which in turn sends signals via the olfactory tract directly to the limbic system, a part of the brain associated with emotions and instincts.