Citrus oils contain a compound that could help treat asthma, new research shows.

Israeli researchers have already had success in lab tests with rats and are currently working on more trials with animals and humans. If the compound, called limonene (search), proves helpful, it could be good news for millions of people worldwide.

Between 100 million and 150 million people have asthma, according to the World Health Organization. In the U.S., more than 20 million people - including about 6 million kids - have asthma, according to the American Lung Association. The numbers have been rising all over the globe for years.

In asthma, airways leading to the lungs are inflamed. The inflammation blocks the airways, making breathing difficult. Allergy triggers can set off asthma. So can irritants such as cigarette smoke and air pollution.

Ozone: Asthma’s Enemy

One of air pollution’s most harmful components is ozone, a bluish toxic gas that irritates lung tissue and causes inflammation. That makes ozone a prime suspect for asthma, says Ehud Keinan of Israel’s Technion-Israel Institute of Technology. Studies have shown that pollution can trigger an asthma attack, especially in kids.

It’s hard to avoid ozone, which pollutes skies all over the world. Instead, Keinan and colleagues tried to thwart ozone’s inflammatory effects.

Their weapon was limonene, an ozone-scavenging compound that occurs naturally in citrus oils. The researchers thought breathing limonene-infused air might help the lungs avoid inflammation.

They tested the idea on rats. One group of asthmatic rats breathed air laced with limonene, which wafted out of an electric scented-oil warmer in their cage. For comparison, another set of asthmatic rats inhaled air scented with a different compound, eucalyptol, which has no effect on ozone.

The rats breathed their scented air nonstop for one week. At the study’s end, the limonene-breathing rats had significantly less airway inflammation and better lung function.

Besides limonene, there are other naturally occurring ozone scavengers. Such plant-based compounds could prompt new ways to control inflammation, say the researchers. Their study appears in the Jan. 15, 2005 issue of Bioorganic & Medicinal Chemistry.