Forty adults were given just three minutes of aromatherapy using two aromas, lavender (considered a relaxing odor) or rosemary (considered a stimulating odor).

The participants were given simple math computations before and after the therapy. The people in the lavender group showed increased beta power, suggesting increased drowsiness, they had less depressed moods, reported feeling more relaxed and performed the math computations faster and more accurately following aromatherapy.

The rosemary group, on the other hand, showed decreased frontal alpha and beta power, suggesting increased alertness. They also had lower state anxiety scores, reported feeling more relaxed and alert, and they were faster (although not more accurate) at completing the math computations after the aromatherapy session.

The finding was reported at the 222nd national meeting of the American Chemical Society, the world's largest scientific society, by an Iowa State University research group.

While they used so-called yellow fever mosquitoes (Aedes aegypti) one of several species of mosquitoes found in the United States Peterson says catnip should work against all types of mosquitoes.

The research led by Peterson put groups of 20 mosquitoes in a two-foot glass tube, half of which was treated with nepetalactone. After 10 minutes, only an average of 20 percent about four mosquitoes remained on the side of the tube treated with a high dose (1.0 percent) of the oil. In the low-dose test (0.1 percent) with nepetalactone, an average of 25 percent or five mosquitoes stayed on the treated side. The same tests with DEET (diethyl-m-toluamide) resulted in approximately 40 percent to 45 percent with eight-nine mosquitoes remaining on the treated side.

In the laboratory, repellency is measured on a scale ranging from +100 percent, considered highly repellent, to -100 percent, considered a strong attractant. A compound with a +100 percent repellency rating would repel all mosquitoes, while -100 percent would attract them all. A rating of zero means half of the insects would stay on the treated side and half on the untreated side. In Peterson.s tests, catnip ranged from +49 percent to +59 percent at high doses, and +39 percent to +53 percent at low doses. By comparison, at the same doses, DEET's repellency was only about +10 percent in this bioassay, he notes.

Peterson says nepetalactone is about 10 times more effective than DEET because it takes about one-tenth as much nepetalactone as DEET to have the same effect.

Most commercial insect repellents contain about 5 percent to 25 percent DEET. Presumably, much less catnip oil would be needed in a formulation to have the same level of repellency as a DEET-based repellent.

Why catnip repels mosquitoes is still a mystery, says Peterson. It might simply be acting as an irritant or they don't like the smell. But nobody really knows why insect repellents work.

Chris Peterson, Ph.D., is a former post-doctoral research associate at Iowa State University in Ames, Iowa, and is now a Research Entomologist with the U.S. Department of Agriculture Forest Service, Wood Products Insect Research Service, in Starkville, Miss.

Joel R. Coats, Ph.D., is professor of entomology and toxicology and Chair of the Department of Entomology at Iowa State University in Ames, Iowa."

Note: This story has been adapted from a news release issued by American Chemical Society for journalists and other members of the public. If you wish to quote from any part of this story, please credit American Chemical Society as the original source.

The most potent extracts eugenol and its related components are stronger even than the commonly used DEET. Indeed, one component is toxic at less than one microgram per square centimeter while DEET requires a concentration of 37.59 micrograms per square centimeter to be effective

Reference: Eun-Hee Kim, Hyun-Kyung Kim & Young-Joon Ahn. Acaricidal activity of clove bud oil compounds against Dermatophagoides farinae and Dermatophagoides pteronyssinus (Acari: Pyroglyphidae). J Agric Food Chem 2003, 10.1021

In a four-week study of how aromatherapy can affect elderly dementia patients, roughly one-third suffered fewer bouts of agitation when they were rubbed with a lemon balm compared to one in 10 who showed improvement when rubbed with an odorless sunflower oil.

"Patients exposed to lemon balm also showed significant improvements in the quality of life, including a decrease in social withdrawal and an increase in constructive activities," study leader Clive Ballard of the University of Newcastle, Newcastle upon Tyne told the conference.

That means the 20-year-old ape Mias gets chamomile on his right ear, basil and angelica on his nose, and fennel, eucalyptus and frankincense on his forehead.

Keepers says the treatment has helped alleviate symptoms from allergies and an upset stomach.

In Allie's case, the 8-year-old primate became depressed when her mother died two years ago. She stopped acting like the silly adolescent she was before her mother's death, but that changed when she started receiving daily aromatherapy.

"When you see how goofy they are, this is how it should be," keeper Rhonda Pietsch said as Allie played in her cage after an oil treatment.

Practitioners of aromatherapy say their oils extracted from plants promote physical, spiritual and emotional health.

The Denver Zoo is believed to be one of the first to try it out on animals.