Exposures to ambient citrus and vanilla aromas showed differential behavioral, psychological and physiological effects. Exposure to citrus resulted in elevated mood, increased physical activity in young adults, and affected food choice. In contrast, exposure to vanilla only affected projected emotions. Some of the effects varied with the subject’s age or with the degree of exposure to the aromas. Even though most of the effects on individual tests are small relative to the estimated effect size, the pattern of results is impressive because it demonstrates that two ambient aromas produce different physiological, psychological and behavioral effects despite their similarity in terms of appeal and intensity. Future tests will explore systematically the effects of other aromas and aroma concentrations to further optimize this test set. Future tests will also include longer exposure durations to verify whether the aroma effects persist or whether they disappear when the novelty effect of the aromas wear off. The outcome of these future studies will contribute to the identification of aromas that are optimized with regard to specific functionalities, such as improved mood, increased relaxation, increased physical activity or other healthy behaviors, including food choice and food intake.
The present study does not investigate possible causalities among the physiological, psychological and behavioral effects, but it has been argued by others that the physiological reactions probably have a psychological origin . Certain aromas, for example, the pleasant ones, have in general positive effects on our mood, whereas others have negative effects. Different effects of mood trigger different physiological reactions. The specific psychological and physiological effects of aromas are not stable, but vary with age, gender, experience and culture. For example, the aroma of Limburger cheese is initially disliked but appreciated with increasing exposure, and the aroma of wintergreen is universally liked in the United States of America and universally disliked in Europe .
Even though the present study is exploratory and limited to only two aromas, the results have some interesting implications. The differences between vanilla and citrus are not self-evident, as the two most probable explanations, namely differences in appeal and in intensity can probably be excluded. Both aromas are pleasant, as indicated by other research  and the aromas were presented at barely detectable levels that were not consciously perceived by most subjects. In addition, both aromas belong to the same general category of food-related aromas. These results suggest, first, that effects of ambient aromas are specific and at least partly independent of intensity, appeal and category and, second, that conscious processing of aromas may not be a necessary requirement for their effect (also suggested by Wexler et al.); and finally, that psychological and behavioral effects seem to be accompanied by physiological effects.