For the more than 20 million Americans suffering from asthma (including 6.1 million children), a cure may be looking no farther than the lemons in your refrigerator.

According to a study at the Technion-Israel Institute of Technology, a key to preventing asthma might be found in a lemon, a rose or a pine tree. In the study, inhalation of limonene, the main component found in the essential oil of citrus, prevented asthma symptoms in animals. The findings were published in the journal Bioorganic and Medicinal Chemistry.

Inspired by previous findings that show the incidence of asthma to be five times higher in urban areas than in rural and agricultural ones, lead researcher Professor Ehud Keinan studied the connection between ozone and asthma and other lung disorders. He believes this higher incidence of asthma is due in large part to the absence of natural “ozone scavengers” produced by plants.

“Ozone in the outer atmosphere is essential for life on earth because it absorbs the destructive ultraviolet radiation emitted by the sun,” he said. “But on earth, it is a dangerous component of air pollution. Numerous studies have shown exposure to ozone, even at low levels, induces airway inflammation and lung injury in humans and animals.”

Keinan’s team also found that ozone is produced in inflammatory tissues by antibodies as a defense against asthma. The presence of this ozone activates more antibodies, perpetuating a vicious cycle.

The research team says that “ozone-scavengers” – substances that devour ozone – could be used for preventing asthma. The inhalation of water-repellent ozone scavengers that accumulate in lung membranes could break the cycle of inflammation. Organic compounds called monoterpenes – produced by all plants – are ideal sources of such substances.

Limonene, an unsaturated monoterpene and the main component in the essential oil of citrus, functions extremely well as an ozone scavenger. Other ozone scavenging monoterpenes studied by the team came from roses, pine trees and citronella, but limonene was the most effective. Saturated monoterpenes, however – such as those found in eucalyptol – were found to have no ozone scavenging properties.

The experiments involved exposing rats with induced asthma-like symptoms to either limonene or eucalyptol for a couple of days. The lung function of the rats showed that limonene inhalation prevented the asthmatic symptoms. The anti-inflammatory effect of limonene was also supported by pathological evidence.