To see if it would improve healing, they performed a standard test where tape is applied and removed repeatedly on the same spot of skin.
To test the impact on their mood, they were asked to complete three standard psychological tests during each session.
To test the impact on stress levels, they also took period blood tests and monitored their blood pressure and heart rates.
Each participant was tested in advance to make sure that each had a normal sense of smell.
Neither the lemon nor lavender oil showed any positive effect on the immune system or on the body's ability to mitigate pain or stress.
But the lemon oil showed a clear mood enhancement, according to the study, which will be published next month in the journal Psychoneuroendocrinology.
"This is probably the most comprehensive study ever done in this area, but the human body is infinitely complex," said co-author William Malarkey, a professor of internal medicine.
"If an individual patient uses these oils and feels better, there's no way we can prove it doesn't improve that person's health," he said.
"But we still failed to find any quantitative indication that these oils provide any physiological effect for people in general."
Source-AFP
SRM/L