Feeling stressed?  The scent of a lemon or any other fragrant plants will help you feel better, say scientists in Japan who report the first scientific evidence that inhaling certain fragrances alters gene activity(!) and blood chemistry in ways that can reduce stress levels.

Their study appears in the Journal of Agricultural and Food Chemistry.

People have inhaled the scent of certain plants since ancient times to help reduce stress, fight inflammation and depression, and induce sleep.   Aromatherapy, the use of fragrant plant oils to improve mood and health, is a popular form of alternative medicine and linalool is one of the most widely used substances to soothe away emotional stress, the authors say.

It's even used to make some fruits and vegetables more appealling. 
tomatoes stress gene activity fragrance
Metabolic engineering of the aroma of tomato fruits is utilized to accumulate the volatile compound S-linalool. The LIS (linalool synthase) gene, under the control of the late-ripening E8 promoter, has been transferred from the Clarkia breweri flowers into the tomato fruits. Diversion of the existing plastid terpenoid pathway leading to carotenoids into the production of S-linalool in ripening tomatoes has been confirmed by GC-MS analysis (Figure 3).

Linalool's actual effects on the body have been a mystery.

Akio Nakamura and colleagues exposed lab rats to stressful conditions while inhaling and not inhaling linalool. Linalool returned stress-elevated levels of neutrophils and lymphocytes, key parts of the immune system, to near-normal levels. Inhaling linalool also reduced the activity of more than 100 genes that go into overdrive in stressful situations.

The findings could form the basis of new blood tests for identifying fragrances that can soothe stress, the researchers say.