People use essential oils, the aromatic compounds created by plants, for a number of therapeutic purposes.  The fragrant oils can be diffused into the air, applied to the skin or ingested through food and drink.

A new study in mice suggests that exposure to orange essential oil may be a nonpharmaceutical way of easing symptoms of post-traumatic stress disorder (PTSD).

For the study, researchers at George Washington University used Pavlovian Fear conditioning to test the effects of orange essential oil on mice exhibiting symptoms of PTSD. Thirty-six mice were split into three groups: 12 received the tone by itself, 12 received water along with fear conditioning and 12 were exposed to orange essential oil by passive inhalation both 40 minutes before and after fear conditioning.

 Usually, when mice have been conditioned and hear a certain tone later they freeze in fear. The study found that freezing behavior in the essential oil group was significantly reduced, and stopped earlier compared to those who received the water and fear conditioning.

Immune cells are a marker of pathways involved in PTSD and the researchers also saw significant differences in the types of immune cells present in the mice that were exposed to orange essential oils, following fear conditioning.

“Relative to pharmaceuticals, essential oils are much more economical and do not have adverse side effects,” Cassandra Moshfegh, a research assistant in Paul Marvar’s laboratory at George Washington University said in a prepared statement. “The orange essential plant oil showed a significant effect on the behavioral response in our study mice. This is promising, because it shows that passively inhaling this essential oil could potentially assuage PTSD symptoms in humans.”

Nearly 8 percent of people will develop PTSD over the course of their lives, according to the U.S. Department of Veterans Affairs.

The specific effects of the essential oil on the brain are not yet clear, but early results suggest differences in gene expression in the brain between mice in the essential oil group and those not.

More studies are needed to determine a definitive mechanism acting on in the brain and nervous system to explain why these effects might help alleviate fear and stress related to PTSD, Moshfegh said.

Moshfegh presented the findings at the Experimental Biology Meeting, held April 22-26 in Chicago.

Contributing Editor/Science Writer