Phantosmia is an olfactory hallucination: a person senses smells that aren’t really there. These imaginary smells can range from unpleasant to enjoyable. Phantosmia can develop into olfactory delusions, which is when a person is constantly affected by these sensory hallucinations. A few diseases and afflictions can cause phantosmia.
Temporal Lobe Seizure
The temporal lobe is the part of the brain responsible for emotions. Immediately before a temporal lobe seizure, people often feel extreme emotions, such as fear or ecstasy. People who experience these types of seizures remain conscious, but they often lose all awareness of time and place. They often don’t realize that they’ve had a seizure. People often experience unnatural sensations before a seizure, including olfactory hallucinations. Phantosmia due to a temporal lobe seizure is referred to as an “aura” or a warning sign that a seizure is about to occur.
Brain injuries, especially those to the temporal lobe, can cause phantosmia in some people. When a brain injury is sustained, the swelling can cause parts of the brain to push against the skull, which can cause more damage. In some cases, phantosmia can occur when certain sensory parts of the brain are damaged.
Certain conditions, such as schizophrenia, can also cause olfactory hallucinations. Schizophrenia can be responsible for a number of different hallucinations, including auditory, visual and gustatory (when foods or beverages taste peculiar). Nerve signals in the brain tell a person with schizophrenia that she is smelling or seeing something that isn’t really there. However, not all schizophrenics suffer from olfactory hallucinations.
People suffering from Alzheimer’s disease most commonly experience auditory and visual hallucinations, but patients have been known to experience olfactory hallucinations as well. These hallucinations are often so real to a person with Alzheimer’s that it is nearly impossible to convince him that the experience isn’t real. Some olfactory hallucinations can be pleasant, such as the smell of flowers or chocolate.
Although rare, phantosmia has been reported in cases of migraine sufferers. In most cases, the smells are unpleasant, but hallucinated smells such as boiling chicken or buttered toast have been reported. Phantosmia usually occurs as an aura before the onset of a migraine. The causes include stress, changes in hormones and some types of foods or medications.