Phantosmia is a phenomenon where people smell odors that are not actually present. It most commonly occurs after a head injury or upper respiratory infection, but can also be caused by seizures, sinusitis, brain tumors, migraines, Parkinson's disease or strokes. Treatments include reassurance, topical or systemic medications, anesthesia to parts of the nose, and rarely surgery to remove olfactory neurons, with endoscopic surgery sometimes allowing a return of the sense of smell after treatment.