a phantom smell or olfactory hallucination is smelling an odor that is not actually there. it is also called phantosmia. it can occur in one nostril or both. phantosmia with unpleasant smells, which is called cacosmia, is more common. it is often described as smelling something that is burned, foul, spoiled, or rotten. experiencing phantom smells from time to time is normal and usually goes away on its own. when hallucinations of this type do not seem to go away or when they keep coming back, this can be very upsetting and can lower an individual's quality of life.