When a smell seems to appear out of nowhere, it can be a confusing and unsettling experience. This phenomenon, which involves perceiving an odor when no physical source is present, is common and scientifically recognized. Understanding the underlying mechanisms and potential triggers can provide clarity on why your nose seems to be sensing a phantom odor.
Defining Phantosmia
The medical term for perceiving a smell that does not exist in the environment is phantosmia, also known as an olfactory hallucination. These phantom odors can be perceived in one or both nostrils and may be intermittent or constant. While some people report pleasant phantom smells, the odors are most frequently described as unpleasant, such as burned toast, chemicals, or a rotten smell. Phantosmia differs from parosmia, which is a distortion of existing smells where the brain interprets a real odor incorrectly.
Causes Originating in the Nasal Pathway
Many instances of phantom smells stem from issues in the peripheral olfactory system, which includes the nose, sinuses, and the olfactory sensory neurons themselves. These peripheral causes typically involve local irritation or damage within the nasal cavity. Inflammation from chronic sinusitis, chronic infection, or allergic rhinitis can cause the olfactory receptor cells to malfunction. Nasal polyps or other growths that obstruct the nasal cavity can also generate these false signals.
Recent upper respiratory infections, including those caused by viruses like COVID-19, are recognized triggers for phantosmia. Post-viral damage to the olfactory receptor neurons can cause a temporary phantom odor. Exposure to environmental irritants, such as insecticides, solvents, or tobacco smoke, can similarly damage the nasal lining and induce phantosmia.
Central Nervous System Triggers
Phantom smells can also signal a disturbance in the central nervous system, where the brain processes and interprets smell information. This is known as central phantosmia, where the issue lies in the brain’s olfactory centers rather than the nose. These central triggers are often more serious, though less common than nasal causes.
One recognized central cause is an olfactory aura, which can precede or accompany a seizure, particularly those originating in the temporal lobe. During this neurological event, the brain’s smell-processing centers are temporarily over-activated, causing the sudden perception of an odor. Migraine sufferers may also experience phantosmia as an aura, a sensory disturbance that occurs before the onset of the headache. Head trauma, neurodegenerative conditions like Parkinson’s disease, stroke, or a tumor affecting the olfactory bulb can also cause phantom smells.
Next Steps and Seeking Professional Help
If you are experiencing phantom smells, it is advisable to consult a healthcare professional to determine the underlying cause. A medical evaluation is particularly important if the phantom smell is sudden, constant, or accompanied by other symptoms such as vision changes, severe headaches, or signs of a seizure. Your provider may conduct a physical examination and a nasal endoscopy, and depending on the suspected cause, refer you to an ENT specialist or a neurologist. Imaging tests like CT or MRI scans may be ordered to check for structural abnormalities in the sinuses or the brain, and treatment is always directed at resolving the underlying condition.