Just follow your nose, it (almost) always knows


Bad odors may be having a negative effect on your mood, behavior and health, even when they’re not consciously registered — and therefore unavoidable.

Ever notice that when you enter a building or a room for the first time, its smell is distinct? Still, you may barely perceive any odor when entering your own home.

What’s going on? It’s not because there are less olfactory molecules floating in the air where you live, but because you have just adapted to the smell. With constant or repeated exposure, sensitivity to certain odors declines.

But even if you can’t sense them, those molecules are being taken in by your body and can have a physiological influence.

Last year, a team of researchers led by Yoshihiko Koga, a professor with the department of neuropsychiatry at the Kyorin University School of Medicine, set out to demonstrate how smells influence brain activity.

Based on an experiment on 20 healthy nonsmoking women with an average age of 21, Koga and his team concluded that, generally speaking, bad smells are bad for you and good smells good.

As part of the study, the team measured the women’s alpha waves — brain-wave currents of between 8 and 13 hertz indicating a relaxed state — by electroencephalograph, or EEG, as they smelled seven different samples.

The samples were: distilled water, a cigarette butt, used cooking oil, a mixture of two types of air freshener, scented fabric deodorizer, natural lavender essential oil and air freshener mixed with isovaleric acid.

The EEG results showed lower alpha wave activity when subjects smelled the cigarette butt, used oil or air freshener with isovaleric acid (which smells like sweaty socks, according to Koga). Lavender oil, the combined air fresheners and the fabric deodorizer resulted in more alpha waves. The distilled water, meanwhile, had no effect.

The experiment suggests that aromas one finds pleasant induce relaxation and that bad odors cause stress. So, Koga notes, “If you are constantly exposed to bad smells that cause you mental stress, your health could be affected in the course of time.”

Of course what makes a smell good or bad is not so simple. Personal preference obviously plays a part, as does past experience and exposure.

When Koga conducted a similar experiment using wine and other smelling samples, for example, the subjects’ level of alpha waves differed depending on whether or not they liked wine.

Meanwhile, some odors override subjective responses, and increase or decrease the brain’s alpha waves regardless of one’s preferences.

In last year’s experiment, the EEG readings for subjects who said they were not particularly fond of lavender indicated that smelling it induced relaxation anyway.

On the other hand, even though some of the women did not find the smell of used cooking oil unpleasant, they experienced a drop in alpha waves.

It is unclear why certain odors have such effects. Koga suggests that, like animals who use their sense of smell to aid their survival, humans have an innate sense that warns them of potentially harmful substances.

“Since humans are animals, I believe their brains unconsciously react to the odors of life-threatening substances, no matter how weak the odors are,” he says.

Research suggests, however, that “good” odors can improve our quality of life if adopted as a treatment.

In Japan, scientific research on the influence of odors on the human body started in the 1980s. Though many riddles about odors remain unsolved, there have been some interesting results.

In 1987, the fragrance company Takasago International Corp. conducted research on how fragrances influence keypunchers’ emotional state and work efficiency. The results suggested that the smell of lemon sharpened the mind and reduced typing errors, rose made workers feel like going to lunch, and jasmine cheered them up when they were getting tired of work in the afternoon.

The effects were apparent, although the smells were subtle and the keypunchers hardly noticed them. Koga says that olfactory molecules exert an effect on the brain even at very low levels.

He is hoping to use fragrance as a supplementary treatment for emotionally troubled people.

“Fragrance is not a medicine,” he said. “Critical mental illness cannot be cured with fragrance alone, but it could work with less serious cases.”

Those who are afflicted with stress-related pains due to overwork, for instance, might be able to ease the symptoms through exposure to certain smells that have a relaxing effect.

“What is good about (treatment with) fragrance is that you could never become addicted, like you might with drugs. Some may become dependent mentally, but at least aromatherapy will never harm your body,” Koga said.