There is convincing evidence that pleasant fragrances can improve our mood and sense of well-being and recent studies have shown that our expectations about an odour, rather than any direct effects of exposure to it, may sometimes be responsible for the mood and health benefits reported.
In one experiment, researchers found that just telling subjects that a pleasant or unpleasant odour was being administered, which they might not be able to smell, altered their self-reports of mood and well-being. The mere mention of a positive odour reduced reports of symptoms related to poor health and increased reports of positive mood!