Temporal lobe epilepsy: Olfactory hallucinations are a common aura symptom in temporal lobe epilepsy, particularly in those with a focus in the medial temporal lobe, which is close to the primary olfactory cortex.

Migraine: Some people experience olfactory hallucinations as part of their migraine aura.
Schizophrenia: Although less common, some patients with schizophrenia may report olfactory hallucinations.
Anxiety or stress: In some cases, intense anxiety or stress can lead to olfactory hallucinations, possibly due to the brain's heightened state of arousal.

Brain tumor: A tumor in the temporal lobe or other areas affecting the olfactory system could cause olfactory hallucinations. Missing this diagnosis could lead to delayed treatment and poor outcomes.
Infectious or inflammatory conditions: Conditions like meningitis or encephalitis can cause olfactory hallucinations and require prompt medical attention to prevent serious complications or death.
Vascular events: Transient ischemic attacks (TIAs) or strokes in areas affecting the olfactory system could present with olfactory hallucinations, making prompt diagnosis crucial to prevent further brain damage.

Parkinson's disease: Some patients with Parkinson's disease may experience olfactory hallucinations, although this is less common.
Alzheimer's disease: In rare cases, Alzheimer's disease can lead to olfactory hallucinations, possibly due to the degeneration of areas involved in olfaction.
Korsakoff's syndrome: This condition, often associated with chronic alcohol abuse and thiamine deficiency, can lead to various hallucinations, including olfactory ones, although this is relatively rare.