Phantosmia: What causes olfactory hallucinations?

Many people are sensitive to certain smells, but in an olfactory hallucination (phantosmia), you detect smells that are not really present in your environment. It should be noted that this term needs to be differentiated from another disorder of sense of smell known as parosmia in which a smell is present in your environment but is distorted.

The smells detected in phantosmia vary from person to person, but may include foul odors such as rotting food or pleasant odors such as fresh flowers.  Phantosmia may progress to olfactory delusions, a condition in which you persistently believe that the smell and its source exist, even though they do not.

Most often phantosmia is due to temporal lobe seizures, but it could also be caused by a brain injury. If you have a temporal lobe seizure, your phantosmia may be brief and you may lose consciousness or have other symptoms of epilepsy.

The combination of phantosmia and olfactory delusions is often due to a psychiatric illness, such as depression or schizophrenia. Phantosmia and olfactory delusions may also occur in people with Alzheimer's disease. Although rare, phantosmia can occur as a symptom prior to a migraine. There is also some evidence to suggest that phantosmia can arise due to a disorder of the smell receptor system rather than the central nervous system.

Because phantosmia can be an indication of a serious illness, consult your doctor if you experience such symptoms.