NEW YORK (Reuters Health) - A key ingredient in the aroma from citrus
fruits such as oranges and lemons appears to protect rats from the
symptoms of asthma, new research shows.

Study author Dr. Ehud Keinan explained that the citrus ingredient is
called limonene, and it likely protects against asthma by "burning"
inhaled ozone, which can increase inflammation in the lungs.

Other scents - such as those emitted from pine trees, geraniums and
roses - contain similar ingredients to limonene, Keinan said, which may
help explain why asthma is much more common in urban areas that lack
vegetation.

"In rural populations, people are very much exposed to these
compounds," he said.

The researcher, who is based at the Technion-Israel Institute of
Technology in Israel, told Reuters Health that squeezing an orange peel
releases liquid that contains a high concentration of limonene. He said
he has heard stories of people who say they experienced relief from
asthma and other lung diseases after spending time around limonene.

He added that he and his colleagues, who report their current
findings
in the journal Bioorganic & Medicinal Chemistry, are currently
investigating how limonene and similar substances may help alleviate
asthma in humans.

A growing body of research suggests that ozone, which is a key
component of air pollution, can encourage changes in the body that
result in persistent inflammation in the airways.

Limonene helps rid the body of ozone because it reacts with ozone,
muting its toxic effects, Keinan explained.

To investigate whether limonene could protect lungs from asthma,
Keinan and his team induced the symptoms of asthma in rats, them let
them smell limonene or eucalyptol, the key ingredient in the odor of
eucalyptus, which does not react with ozone.

The researchers checked the rats for asthma symptoms repeatedly over
a
period of 20 hours to five days. They found that only rats exposed to
limonene "didn't show any symptoms of the disease," Keinan said.

These results suggest that inhaling limonene may protect people from
developing asthma, or alleviate symptoms in those already diagnosed, he
noted.

SOURCE: Bioorganic & Medicinal Chemistry, December 8, 2004.