Smell is our most primitive sense, directly affecting the limbic system, the section of our brains involved with sex, motivation and emotion. According to proponents of aromatherapy, we can harness this connection by using scents we find calming, pleasing or uplifting. Yet mainstream physicians in North America debate the health benefits touted in the field of aromatherapy, largely citing a lack of rigorous, scientific study for the claims of aromatherapy, which are drawn mainly from anecdotal case studies and folklore.

However, good research on aromatherapy has been published, primarily in Germany and Japan. It probes the effects, on both mind and body, of inhaling essential oils or applying diluted forms of them to the skin. The research shows that, indeed, there is something to the practice of healing through aromatherapy.

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Before describing some of the most intriguing studies (all of which involve human use of various aromatherapies, unless otherwise noted), a word of caution is in order: Plants vary. People vary. And any living organism will react according to both genetics and environmental factors. It shouldn’t be a surprise, then, that some people have strong reactions to some essential oils, while others have no reaction at all, and that sensitivities can vary over time. Also, just because an oil is natural doesn’t guarantee that it’s safe—imagine the consequences of giving a massage using “all-natural” poison ivy! Here’s a summary of some of the studies that have been conducted on aromatherapy’s benefits.

Researchers at the Toho University School of Medicine in Tokyo measured the shift of brain waves when inhaling jasmine oil, and found it produces a stimulating effect similar to that of coffee.

Based on computer measurements of subtle and rapid reactions, researchers at the University of Innsbruck in Austria concluded that inhaled lavender oil sedates the central nervous system.

In a study at the University of Vienna, researchers focused on the effect of several oils on mice that had been overagitated by caffeine. The team found that the scents of lavender oil, lime blossom, neroli oil and East Indian sandalwood oil sedated the mice.

Japanese researchers have found that inhaling the odors of orange oil or Taiwan hinoki oil (Chamaecyparis taiwanensis) decreases blood pressure, and that inhaling the odors of peppermint and jasmine oils reduces peripheral blood pressure. Researchers at International Flavors & Fragrances in Union Beach, New Jersey, found that inhaling nutmeg oil odor reduces blood pressure in response to stress.

Researchers at Ernst-Moritz-Arndt University in Griefswald, Germany, found that essential oils in general are local anesthetics when inhaled in very low doses because of their fat-soluble nature, which means that they easily alter cell membranes.

At the neurological clinic of the Christian Albrechts University in Kiel, Germany, researchers found that a combination of peppermint oil and eucalyptus oil significantly relieves headache pain in humans.

Researchers in Japan found that bitter orange odor makes it easier to fall asleep while under stress (they linked it to an inhibition of the excitement of the central nervous system).

Researchers at the Free University of Berlin found that people who use hops pillows inhale the hop constituent 2-methylbut-3-en-2-ol from the pillow, which is a sleep-inducing agent in pharmacological trials.

People who inhale chamomile shift from describing images in negative terms to describing them in positive terms, according to researchers at the University Department of Experimental Psychology at Cambridge University.

Can Science Really Prove Aromatherapy’s Value?

The principles of aromatherapy are, scientifically, very hard to study and prove. Normally the goal in scientific studies is to remove all variables to account for only one effect. But massage, touch, music, lights, words and pleasant surroundings can all contribute to modify the mood in aromatherapy. Also, patients seeking aromatherapy are often psychologically predisposed to an effective treatment. Another fact to consider is that natural essential oils may consist of almost 300 different constituents, and these act in both a synergistic and antagonistic manner, yet scientific studies focus on only one constituent at a time. Add to this already- complicated equation the choice of parameters researchers choose to measure, namely, the metabolism of oils, the study participant’s body fat, the variation among individuals and so on, and you can see why a proper experiment is extremely difficult to design and execute.

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As scientists, we know that psychological stress causes the release of adrenaline and cortisol, which, in turn, suppress immune responses. This leads to more infection and further emotional depression. So if a particular treatment makes us feel good, does it not then provide a positive influence on our immune systems? Whether the final results are a placebo effect or not, in the final analysis the question must be asked: If it improves a condition without doing harm—and at a reasonable price—is it not of value? Until science provides more answers about aromatherapy, we may do best to rely on both anecdotal findings and scientific research as it emerges.

—Arthur O. Tucker

The Scent-Body Connection

The effects below are supported by research. Please remember that using essential oils requires caution—some can irritate or do harm, especially if you are sensitive or allergic to constituents within these oils.

Stimulating: Jasmine, rosemary, dwarf pine

Calming: Lavender, East Indian sandalwood, chamomile, lemon balm, valerian, neroli

May reduce headache severity: Peppermint, eucalyptus

May improve test performance: Peppermint, vanilla

Sleep aids: Lavender, bitter orange, hops

May reduce blood pressure: Peppermint, jasmine, nutmeg

Aromatherapy While Sleeping

Some research focuses on the effects of inhaled essential oils on sleep. Researchers at Bowling Green State University in Ohio found that people are more responsive to odors when sleeping than when awake. Jasmine and peppermint odors both disrupt sleep; androstenone (a key component of human body odor) was by far the most disruptive of the odors tested.

Further, they found that androstenone, peppermint and ‘Grosso’ lavandin (hybrid lavender) odors affect dream content and brain-wave activity, and the odors are sometimes incorporated into dreams. German researchers found that inhaled orange oil not only produces a positive effect on dream content but also causes significant increases in heart and respiration rates. The latter study also incorporated skatole, a common odorant of feces, and human vaginal secretions in a pilot study involving seven men. Skatole produced very negative dreams; the reaction to the female odors varied by individual.

Our Advice: Essential Oil Safety

Wise use of essential oils means recognizing that they are highly concentrated, so they can irritate if not used properly.

Always keep essential oils out of the reach of children and pets, and wash your hands thoroughly after working with them.

Always mix an essential oil with a carrier oil, such as almond oil. Use 1 to 3 drops of essential oil for every teaspoon of carrier oil. Store any unused mixture in a dark glass container in a cool place.

Because essential oils are volatile and concentrated, they are also highly flammable. Keep them away from lit candles and other flames.

Essential Oils to Use with Caution

Essential oils are not inert. They change when isolated in the lab or when they come into contact with the body, either through inhalation or absorption by the skin. Lemon verbena oil, for example, contains two allergens formed during distillation. Safrole, the active ingredient of sassafras oil, is not carcinogenic by itself, but can quickly metabolize to become several compounds that quite definitely can cause liver cancer.

Scientific journals, including Contact Dermatitis, are full of documented reactions to many essential oils, but several fragrance ingredients stand out as the causes of repeated problems. The International Fragrance Association (IFRA) has issued warnings against the essential oils listed below.

Angelica root oil

Cassia oil

Chenopodium oil

Cinnamon oil

Citrus oils (especially bergamot, bitter orange, lemon and lime)

Costus root oil

Fig leaf absolute (absolutes are alcohol-soluble perfume materials)

Lemon verbena oil

Marigold oil and absolute

Oak moss absolute and resinoid

Opopanax oil

Peru balsam oil

Oils of pine, balsam fir and other members of the Pinaceae family

Sassafras oil

Savin oil

American and Asian styrax