The smell of happiness.

Here's an interesting bit. de Groot et al. obtained armpit sweat from 12 young Caucasian heterosexual men in three consecutive sessions (with fear-inducing, happiness-inducing, or neutral film clips), separated by a week's interval. 36 female Caucasian undergraduates served as "receivers" of the odor stimuli. Exposure to sweat from happy senders elicited a happier facial expression than did sweat from fearful or neutral senders; further, sweat from happy senders elicited a more global processing style relative to sweat from fearful senders. Here is their abstract:

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.