You may be experiencing phantosmia or "phantom smell," also called "olfactory hallucination" and defined as smelling something that simply isn't there.
In August 2009, The New York Times published an article by a woman who smelled dirt all the time, which she at first attributed to her potted plants until she found that the smell followed her where ever she went, even when no dirt or potted plants were nearby. Once she learned that she suffered from phantosmia, she had a round of medical tests, including "an M.R.I. of my brain (ruling out a tumor), a CT scan of my sinuses (to check for infection), and finally an EEG," because olfactory hallucinations can occur with seizure disorders. She received a clean bill of health and about a year later realized that the smell was gone. But then the smell of burnt chili replaced the smell of dirt eventually to be replaced by the smell of lavender.
Phantosmia can be associated with certain illnesses - in addition to epilepsy, it has been seen in persons who eventually develop Parkinson's and in others with brain tumors. And it may occur in patients suffering from depression or schizophrenia and, sometimes, in those with Alzheimer's disease. But just because phantosmia happens in individuals with these disorders doesn't mean that all cases are related to serious illness. From what I've read, I understand that phantosmia often arises because of a loss of some of the ability to smell normally. The New York Times article quoted Donald Leopold, M.D., chairman of the department of otolaryngology at the University of Nebraska, who has been studying olfactory disorders for 30 years. According to Dr. Leopold, with impairment of the ability to smell, the brain overcompensates by offering up odors, usually disagreeable ones. When this happens, certain neurons, which previously had blocked such odors, turn off.
The good news is that phantosmia often disappears without treatment. You might want to consult an ear, nose and throat specialist with experience in treating distortions in smell. Available treatments include nasal saline drops, antidepressants, antiseizure medications, and sedatives. If all else fails and patients can no longer deal with the unwelcome smell, surgery to sever a portion of olfactory connections can help resolve the problem.
Andrew Weil, M.D.