Aromatherapy -- the use of plant oils to improve well-being -- sounds lovely, doesn't it? How wonderful if a whiff of lavender could make you feel drowsy, or a little dab of rosemary oil could relieve muscle pain.
There's certainly a plausible biological basis for the idea that smells can have direct effects on the body. On the yucky side, for instance, nothing makes me nauseated more quickly than the odor of those pine tree-shaped "air fresheners" that taxi drivers hang in their cabs. On the positive side, for me, the scent of a fresh Christmas tree always evokes warm memories of childhood; or the smell of cookies baking in the oven can help sell a house.
But there's little solid science behind many of the claims of medical benefit from aromatherapy, which usually means soothing the body through smells, but can also mean rubbing plant oils on the skin.
"There have been some pretty wild claims" about the effects of aromatherapy, said Dr. Charles J. Wysocki , a behavioral neuroscientist at the Monell Chemical Senses Center, a corporate-sponsored research institute in Philadelphia, who has spent more than 30 years studying smell.
It is precisely this lack of data that makes aromatherapy so important to study, said Ohio State University health psychologist Janice Kiecolt-Glaser. She is currently analyzing her results from a government-funded study in which she exposed one group to lavender, "which is supposed to be a relaxant," she said, another to lemon, "which is supposed to be stimulating or uplifting," and the third group to distilled water, which has no smell.
There is so little data supporting aromatherapy that the National Center for Complementary and Alternative Medicine, a branch of the government, does not even discuss aromatherapy on its website, though the agency is now funding one study: Kiecolt-Glaser's.
Proponents of aromatherapy point to several studies that they claim show it works. Some data do suggest that pleasant odors such as rose, jasmine, and lavender might lower blood pressure, and a small study suggests that lemon oil might reduce the doses needed of antidepressants. But these studies were not rigorous.
Some better-designed studies, using placebo smells for comparison, showed no medical benefit from aromatherapy.
A 2001 study of 33 patients with postsurgical nausea found that oil of peppermint was no better than rubbing alcohol or saltwater in providing relief. A 2002 study of 17 hospice patients found that using a humidifier with plain old water was just as effective (and not very effective at that) as water with lavender oil in relieving anxiety and pain. A randomized, double-blind study in 2000 of 66 women awaiting abortions found that aromatherapy with essential oils (vetivert, bergamot, and geranium) was no more effective than a placebo smell (hair conditioner) at relieving anxiety. A 2003 randomized study of 313 cancer patients undergoing radiation similarly concluded that aromatherapy was psychologically "not beneficial."
Worse yet, a study of 60 healthy men and women, published this year in Psychosomatic Medicine, showed that those exposed to either a pleasant odor (lemon) or an unpleasant odor (machine oil) actually had a greater response to experimentally induced pain than those exposed to no odor.
"It's very difficult to demonstrate positive effects" from odors, said Wysocki. By contrast, "it's very easy to demonstrate mood swings in the negative direction. If you expose people to nasty-smelling odors, they will get upset. If you expose them to vomit, some people will actually get sick and vomit."
Perhaps that's because the brain is hard-wired to detect "bad" smells -- those like the smell of rotting food -- that could signal danger.
Reactions to smells are also highly conditioned. "A child who experiences the smell of roses for the first time on a summer walk in the garden with his mother will have different memories of the smell of roses than a child who first experiences the smell of roses at his mother's funeral," said Wysocki.
Expectations also play a huge role in reaction to smells. In one of his own studies, Wysocki divided subjects into groups of 30 each and exposed them to the same, unknown smell. People in one group were told they were getting aromatherapy and they quickly got used to the smell and soon stopped smelling it at all, while a group that was told the smell could be dangerous in high concentrations was increasingly bothered by the odor as time went on, he said.
Because people expect a benefit from aromatherapy, it may help them feel better, said Cherie Perez , a research nurse supervisor at the University of Texas M.D. Anderson Cancer Center in Houston.
But it's tough to pin down what's going on when someone feels better after a massage with lavender oil, she said. Is it the massage? The oil being absorbed into the skin? The smell of the oil? The attention of the masseuse? All of the above?
My take on this? Enjoy a nice, warm bath if you want to relax. But don't count on the expensive bath oil to help anyone but the company that sold it to you.
Judy Foreman is a freelance columnist who can be contacted at firstname.lastname@example.org.