Pain tolerance selectively increased by a sweet-smelling odor

The mechanism underlying reported analgesic effects of odors in humans is unclear, although odor hedonics has been implicated. We tested whether odors that are sweet smelling through prior association with tasted sweetness might influence pain by activating the same analgesic mechanisms as sweet tastes. Inhalation of a sweet-smelling odor during a cold-pressor test increased tolerance for pain compared with inhalation of pleasant and unpleasant low-sweetness odors and no odor. There were no significant differences in pain ratings among the odor conditions. These results suggest that smelled sweetness can produce a naturally occurring conditioned increase in pain tolerance.