It is well known that feelings of happiness transfer between individuals through mimicry induced by vision and hearing. The evidence is inconclusive, however, as to whether happiness can be communicated through the sense of smell via chemosignals. As chemosignals are a known medium for transferring negative emotions from a sender to a receiver, we examined whether chemosignals are also involved in the transmission of positive emotions. Positive emotions are important for overall well-being and yet relatively neglected in research on chemosignaling, arguably because of the stronger survival benefits linked with negative emotions. We observed that exposure to body odor collected from senders of chemosignals in a happy state induced a facial expression and perceptual-processing style indicative of happiness in the receivers of those signals. Our findings suggest that not only negative affect but also a positive state (happiness) can be transferred by means of odors.

Odor and lateralization (irritation) thresholds (LTs) for ammonia vapor were measured using static and dynamic olfactometry. The purpose of the study was to explore the test-retest reliability and comparability of dynamic olfactometry methodology, generally used to determine odor thresholds following European Committee for Standardization guidelines in the context of odor regulations to outside emissions, with static olfactometry. Within a 2-week period, odor and LTs for ammonia were obtained twice for each method for 24 females. No significant differences between methods were found: mean odor detection thresholds (ODTs) were 2.6 parts per million (ppm) for either method (P = 0.96), and mean LTs were 31.7 and 60.9 ppm for the static and dynamic method, respectively (P = 0.07). Test-retest reliability was higher for the dynamic than for the static method (r = 0.61 vs. 0.14 for ODTs and r = 0.86 vs. 0.45 for LTs). The choice of optimal method for any application, however, depends not only on psychometric factors but also on practical factors such as physicochemical properties of the compound, availability of equipment and expertise, task efficiency, and costs.

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Some individuals ascribe health symptoms to odor exposures, even when none would be expected based on toxicological dose-effect relationships. In these situations, symptoms are believed to have been mediated by beliefs regarding the potential health effects from odorants, which implies a controlled type of information processing. From an evolutionary perspective, such a form of processing may hardly be the only route. The aim of the present study was to explore the viability of a fast and implicit route, by investigating automatic odor-related associations in the context of health. An Implicit Association Test assessing association strengths between the concept odor and the concepts healthy and sick was conducted. Three experiments (N=66, N=64, and N=64) showed a significantly stronger association between the concepts odor and sick than between odor and healthy. These results did not match explicit associations and provide evidence for a fast and automatic route of processing that may complement consciously controlled processes. A dual-processing theory of olfactory information is proposed leading to new hypotheses regarding the development and maintenance of odor-induced health symptoms.

Associations between certain odors and for instance health effects may lead to positive or negative attitudes toward these odors. However, in experiments we conducted using the Implicit Association Test (IAT), we encountered attitudes even to odor "words." The IAT is based on the principle that reaction times measuring the association between words from a target dimension (in this case, odor vs. a neutral reference category) and an attribute dimension (i.e., positive or negative words) reflect the attitude to the target, where attitude-congruent associations between target and attribute are reflected by shorter reaction times. In a first experiment, we found distinctly positive attitudes to the concept odor in a student sample, which was replicated in a second experiment. In the main experiment, subjects in the aromatherapy group, who prefer using scented consumer products for relaxation purposes, showed a significantly more positive attitude toward odor words in the IAT than a control group, who did not have such a preference. The fact that results from the implicit test were not always associated with explicitly stated attitudes toward the odor words attests to the fact that the IAT measures the attitude of interest in a different way. As such, the IAT has added value in circumstances where explicit tests can be biased.