Olfacan was a substance used by Starfleet medical personnel. It was a nasal anesthetic that could block out unpleasant odors when smeared under the nose.
Julian Bashir used olfacan when he was a member of an away team to the planet that had been dubbed "Armageddon" due to frequent comet impacts on the surface. Kira Nerys refused it point blank, and Jadzia Dax received no benefit due to Trill biology not responding to the contained anaesthetic. (DS9 - Day of Honor novel: Armageddon Sky)