Smell affects everything that defines a human. It can even help us heal.
Our most primitive sense is smell. It directly affects the limbic system, that section of the brain involved with sex, motivation, and emotion—in short, almost everything that defines us as human. Yet mainstream physicians in North America debate the real value of scents, specifically the healthful benefits touted in the growing field of aromatherapy. The skepticism is based largely on the 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 during the past decade, primarily in Germany and Japan. It probes the effects, on both mind and body, of inhaling herbal essential oils or applying diluted forms of them to the skin, as well as the effects of individual essential oil components. The research shows that, indeed, there is something to healing through aromatherapy.
Before describing 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 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 natural poison ivy! Add heat and light, and the likelihood of an allergic reaction increases astronomically.
It’s difficult to interpret essential oils’ beneficial and harmful effects, and contradictory conclusions abound. But the easiest studies to interpret are those involving electrical rhythms of the brain known as alpha waves, dominant in meditation and other relaxed states, and beta waves, which are associated with alert states and a sign of anxiety and apprehension.
Japanese researchers have found that inhaling lavender and sandalwood oils increases alpha-wave activity (relaxation), while inhaling jasmine oil increases beta-wave activity (alertness, anxiety). Researchers at the Toho University School of Medicine in Tokyo supported this finding by measuring the upward shift of brain waves. The measurements show that inhaled jasmine produces a stimulating effect similar to that of coffee. In contrast, they found that East Indian sandalwood oil produces a calming effect. From skin-reaction tests, the Toho team also found that the scent of chamomile oil calms, while jasmine stimulates.
But Tyler Lorig, a psychologist now at Washington and Lee University in Virginia, examined these measurements in more detail and found that brain-wave patterns can be affected by the beliefs and thoughts about the stimulus, suggesting that the Toho team’s findings may be deceiving. To quote the cliché, more research needs to be done.
Beyond its impact on electrical activity of the brain, aromatherapy may have an impact on other body systems. Mice who inhale oils of rosemary and dwarf pine become more active, but when they inhale oils of lemon balm and valerian, they calm down, according to researchers at the Institute of Pharmacology in Tübingen, Germany. 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 (and its main constituents, linalool and linalyl acetate), lime blossom, neroli oil, and East Indian sandalwood oil sedated the mice. The researchers also found that lavender oil is quickly absorbed through human skin, and the highest level of linalool in the blood can be detected within twenty minutes after a massage.
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. Further, they found that inhaling lavender oil causes significant increases in reaction time, but inhaled jasmine significantly decreases it.
And 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.
Stress produces chemical changes that can be measured, including an increase of ACTH (adrenocorticotropic hormone) in blood plasma. Researchers at the Tokyo University of Pharmacy and Life Sciences in Japan found that inhaling chamomile oil odor reduces plasma ACTH in rats.
Other 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; this resulted in a U.S. patent for a stress-reducing fragrance with nutmeg.
Researchers have also investigated the potential of essential oils to relieve headaches. Previous research shows that applying one or two drops of peppermint oil to the temples not only produces a cooling effect by altering calcium channels of the body’s cold receptors, but also inhibits serotonin and substance P (the body’s pain messengers) in smooth-muscle contraction and significantly increases skin blood flow in animals. At the neurological clinic of the Christian Albrechts University in Kiel, Germany, researchers went further and investigated a combination of peppermint oil and eucalyptus oil in ethanol and found that the combination significantly relieves headache pain in humans.
Additional research included other parameters of stress, such as constriction of peripheral blood vessels, heart rate, muscle tension, pupil dilation, startle response, and frequent headaches. However, the results are often difficult to interpret; sometimes the results are contradicted by other publications, sometimes the researchers used synthetics and/or isolates, and sometimes the researchers did not specify the fragrances beyond “pleasant” or “unpleasant.” Again, more research needs to be done.
Leaves of aromatic plants contain glands filled with fluids known as essential oils. Sunlight causes the glands to burst, releasing the scent-filled oil, which quickly turns from liquid to gas. This quick evaporation is called volatility.
Researchers at the University of Cincinnati have found that inhaling the scent of peppermint improves performance in college students who had trouble concentrating for long periods. This finding was further supported by an increase in skin conductance (a measurement used in lie-detector tests) when the students inhaled peppermint oil, indicating an increase in involuntary arousal. But the researchers concluded that the positive effects of inhaled peppermint oil were due to students gradually allocating their attention, rather than to any increase in arousal.
On the other hand, Tyler Lorig also investigated peppermint as well as vanilla; his findings suggest that peppermint oil fragrance increases arousal, while vanilla increases arousal in females but not males (the researchers didn’t explore the sexual differences for reaction to vanilla odor).
Some research also focuses on the effects of inhaled essential oils on sleep. Researchers at Bowling Green University in Ohio found that people are more responsive to odors when sleeping than when awake. Jasmine and peppermint odors both disrupt sleep, and androstenone (a key component of human body odor usually described as “musky”) 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 auxiliary and vaginal secretions in a pilot study involving seven men. Skatole produced very negative dreams, but the reaction to the female odors varied by individual.
As for using aroma as a sleep aid, researchers in Japan have 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). And hops pillows, long advocated by herbalists to promote sleep, have been scientifically proven to work: 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 indeed a sleep-inducing agent in pharmacological trials.
Finally, Japanese researchers found that inhaling Taiwan hinoki oil decreased anxiety, fatigue, depression, and hostility; 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.
Maybe you remember, as I do, the smell of Vicks VapoRub from your childhood. My mother smeared it on my chest and neck when I had a cold. Vicks is an old standby, an over-the-counter remedy that people turn to because it is effective. Its active ingredients are camphor, menthol, and eucalyptus oil; its inactive ingredients (those that are there to enhance or support the active ingredients) are cedarleaf oil, nutmeg oil, thymol, special petroleum, and spirits of turpentine. Most of its ingredients are herbal essential oils, which have been used widely for years to treat colds. People use Vicks as a decongestant—the odor helps clear the passageways—not for its germ-fighting effects. But research is beginning to explore essential oils’ ability to fight germs, although only a few relate directly to human application and specifically to aromatherapy.
Researchers at the University of La Laguna in Tenerife, Spain, found that in test tubes the oil of Balm of Gilead (Cedronella canariensis) inhibits the growth of Bordetella bronchiseptica, a bacterium that causes illness in the respiratory tract. It also inhibits Cryptococcus albidus (a pathogenic fungus), and the oil is superior to Nystatin (a fungus-fighting pharmaceutical) in controlling all of the organisms tested. This may justify the popular use of Balm of Gilead in the Canary Islands as a decongestant and germ-fighter for certain diseases of the respiratory tract.
One additional study is worth mentioning: Researchers in Japan and Paraguay investigated oil of spike lavender (Lavandula latifolia) by applying it to the skin of rats; they concluded that it is anti-inflammatory because it inhibited tissue swelling.
In scientific studies, all variables are normally removed to account for only one effect. In aromatherapy, these variables include the very essence of perceived effect in a holistic approach: Believing that something works, combined with the totality of the experience, helps make it so.
Massage, touch, music, lights, words, and pleasant surroundings all contribute to modify the mood in aromatherapy. Also the 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 that 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.
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 system? 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.The Scent-Body Connection
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