At last! The reason that some of us love the smell of mothballs and others can’t stand it.

Researchers from Brown University in Providence, R.I., report that our responses to certain odors are based on past experiences with the scent.

“Most people assume we all like the smell of roses and hate the smell of skunk,” lead researcher Rachel Herz, PhD, a visiting assistant professor of psychology at Brown, tells WebMD. But “with the exception of irritating odors, smell is something we come to know from personal and cultural experiences.”

In one experiment of 30 women, participants played a computer game in the presence of a custom-made, slightly unpleasant scent that mixed dirt, rain, and hot buttered popcorn. If participants had a good time playing the game, they were more likely to report liking the odor they smelled. If they didn’t like the game, they didn’t like the scent.

“We come to smell with a blank slate, and why we like or dislike it has to do with experiences,” Herz says.

The study appears in the December 2004 issue of the International Journal of Comparative Psychology.

In the second experiment, 36 men and women tested two new scents, one slightly floral, the other clean and watery. In a pretest, they rated these scents as well as rose, vanilla, lemon, and peppermint. Participants rated the new scents as both unfamiliar and pleasant.

But not for long.

One group entered a scented room and played a frustrating computer card game replete with annoying sound effects and losing hands. By contrast, another group sat in a scented room and read magazines.

In both groups, half were exposed to the floral scent, the other half to the watery one. The third group played the computer game in an odorless room. All participants either played the computer game or read magazines in three sessions spread out over the course of a week. After each session, they rated the six scents.

Participants were more likely to score the pleasing new odors as distasteful after playing the frustrating game.

The bottom line from both experiments is that when an odor is paired with an emotional event, perception of that odor is altered to fit that association.

“This study contributes quite a lot to the study of smell because very little has been done in terms of any direct experiments that look at how or why it is we like/dislike smells,” she says.

Although little empirical data exist, Herz says, cultural studies back up the new results. Consider that Americans tend to like the smell of wintergreen, a common ingredient in candy and gum, but in Britain, where wintergreen is often used to make medicine, the odor is less pleasing. There are, however, a few exceptions to this theory. Irritating odors, such as ammonia, may be immediately disliked when smelled, and individual genetic differences may also play a role in emotional responses to odors.

The Future Smells Bright

In the future, retailers and restaurateurs may use signature scents to create positive associations for consumers, Herz says.

“In hospitals, people who are more positive recover quicker than those with negative outlooks,” she says. “We could use a smell that an individual finds pleasant and it may help them feel better, or we can tie a new smell to feelings of wellness,” she says.

Alan R. Hirsch, MD, neurological director of the Smell and Taste Treatment and Research Foundation in Chicago, tells WebMD that the use and role of smells will clearly grow in the coming years.

In general, smells can help people lose weight, boost sexual arousal, increase speed of learning, reduce severity of migraine headaches, and even quell claustrophobia, says Hirsch, who has conducted numerous experiments on how scent affects behavior, mood, and perception.

And “more and more companies will seek to have an aroma that is associated with a specific product the way that Play-Doh has a specific smell that makes people recall childhood,” he says.

For example, “Lemon Pledge may not clean any better than regular cleaners, but people smell it and assume it means a clean bathroom,” he says.

“We will see more and more odors used to brand products,” he says. He predicts that in 10 to 20 years, all products will be branded to a specific odor.

By Denise Mann, MS, reviewed by Michael W. Smith, MD

SOURCES: Herz, R.International Journal of Comparative Psychology, December 2004. News release, Brown University. Rachel Herz, PhD, visiting assistant professor of psychology, Brown University, Providence, R.I. Alan R. Hirsch, MD, neurological director, Smell and Taste Treatment and Research Foundation, Chicago.