March 5 (HealthDay News) -- Aromatherapy: It may smell good, but is it actually good for you?

Researchers are reporting that two of the most commonly used scents in aromatherapy do nothing to heal wounds, relieve pain or enhance immune status, although one did briefly improve mood.

In fact, in some cases, distilled water showed more of a salutary effect, the study found.

"Keep it in mind before spending a lot of money" on aromatherapy, said study lead author Janice Kiecolt-Glaser, director of the Division of Health Psychology at Ohio State University. "I buy perfume, because I like the smell. If you enjoy the smell, that's one thing, but don't buy perfume because you expect to change your physiology or to really influence your health."

The study results are published online in the April issue of the journal Psychoneuroendocrinology.

Used for thousands of years in countries such as India and Egypt, aromatherapy has many adherents who say the concentrated oils extracted from flowers improve health and emotional well-being, according to the Cleveland Clinic.

Despite its widespread use, there's little scientific data on the effectiveness of the therapy, the study authors stated.

"This is by far the largest and most comprehensive study of actual physiological outcomes," Kiecolt-Glaser said. "There are different perspectives on why odors should work in terms of changing physiology, if they do. A lot of aromatherapy literature thinks of it as a drug-specific mechanism." In other words, that scents work much like drugs work, with very specific effects.

Using this point of view as a starting point, Kiecolt-Glaser and her colleagues, who included husband Dr. Ronald Glaser, looked at the two odors that have been most researched: lemon, which is purported to be stimulating and a mood enhancer, and lavender, which is supposed to be relaxing and is used as a sleep aid. Distilled water was used as a control.

Potential study participants were first screened to see if they had an adequate sense of smell. Fifty-six people were then admitted into the study. During three half-day sessions, half the group was handed an envelope that explained the scent they were about to smell and what to expect. The other participants were simply told they'd be smelling a variety of fruit and floral odors.

Then the researchers taped cotton balls laced with either lemon oil, lavender oil or distilled water below the volunteers' noses for the duration of the tests. The participants were monitored for blood pressure and heart rate, and the researchers took regular blood samples from each volunteer. The samples were analyzed for changes in different biochemical markers, including Interleukin-6 and Interleukin10, as well as the stress hormones cortisol and norepinephrine.

The researchers then tested the volunteers' ability to heal by using a standard test in which tape is applied and removed repeatedly on a specific site on the skin. The scientists also tested the volunteers' reaction to pain by placing their feet in 32-degree water. Finally, the participants filled out three standard psychological tests to assess mood and stress during each session.

While lemon oil showed a clear mood enhancement, lavender oil did not, the researchers said. Neither smell had any positive impact on any of the biochemical markers for stress, pain control or wound healing.

SOURCES: Janice Kiecolt-Glaser, Ph.D., professor of psychiatry, and director, Division of Health Psychology, Ohio State University, Columbus; April 2008, Psychoneuroendocrinology