Phantosmia, or an olfactory hallucination, is the sudden, often unsettling perception of a strong, foul odor that is not actually present. This experience typically involves the phantom smell of something unpleasant, such as decay, burning rubber, spoiled food, or sewage, which is why people often describe the sensation as “smelling death.” While the experience itself is disturbing, phantosmia is a symptom that points toward a disruption in the olfactory pathway, not a freestanding diagnosis. The root cause of this phantom scent can originate from issues in the nose itself or from the central nervous system, where smell signals are processed.
Localized Sources of Phantom Smells
The most common origins of phantosmia are localized in the upper respiratory tract, where the olfactory sensory neurons are located. Chronic inflammation from conditions like sinusitis can physically damage the delicate nerve endings within the olfactory epithelium high in the nasal cavity. This damage can cause the neurons to misfire, generating an electrical signal that the brain interprets as a smell, even though no odor molecules are present.
Nasal polyps, which are noncancerous growths in the lining of the nasal passages or sinuses, also contribute to this phenomenon. These growths can physically obstruct the normal flow of air and mucus, leading to persistent irritation and inflammation of the olfactory apparatus. Similarly, a severe upper respiratory infection or dental abscesses that extend into the sinus cavities can temporarily injure the olfactory nerve.
In these peripheral cases, the phantom smell is often described as being stronger in one nostril than the other, which can be a distinguishing clue for diagnosis. The physical irritation or injury to the olfactory nerve leads to a chaotic signal transmission, resulting in the perception of metallic, chemical, or rotting odors. Treating the underlying nasal or dental condition, such as clearing the infection or reducing inflammation, often resolves this type of phantosmia.
Neurological and Systemic Drivers of Olfactory Hallucinations
When the source of the phantom odor is not in the nose, the cause is related to the central nervous system, involving how the brain processes scent information. One such driver is the olfactory aura, a sensory warning that precedes a migraine headache for some individuals. This brief hallucination of a smell, often burnt or foul, is caused by abnormal electrical activity spreading across the brain’s cortex before the headache phase begins.
Temporal lobe seizures are a neurological cause where the phantom odor is frequently the first sign of a seizure. Since the temporal lobe houses the primary olfactory cortex, abnormal electrical discharges in this region can directly trigger a vivid, brief smell hallucination.
Head trauma, such as a concussion or traumatic brain injury, can also damage the olfactory bulb or the neural pathways leading to the temporal lobe, creating persistent or intermittent phantom smells. In rare instances, phantosmia may indicate a brain tumor or lesion pressing on the olfactory structures. Systemic issues, including certain medications, systemic infections, or neurodegenerative diseases like Parkinson’s, can also disrupt the complex neurochemistry involved in smell perception, leading to these phantom odors.
When to Consult a Specialist and What to Expect
Any persistent or recurring experience of phantosmia warrants a professional medical evaluation to determine the underlying cause. It is particularly important to seek prompt attention if the phantom smell is sudden, occurs only in one nostril, or is accompanied by other neurological symptoms. These warning signs include:
- Double vision
- Weakness
- Loss of consciousness
- Severe headaches not typically associated with migraine
A general practitioner will typically refer a patient to an Otolaryngologist, a specialist for the ear, nose, and throat (ENT), to investigate peripheral causes. The ENT specialist may perform a nasal endoscopy, using a small camera to visually inspect the nasal passages and sinuses for signs of infection, polyps, or tumors. If the nasal examination is inconclusive, the patient may be referred to a neurologist.
The neurologist may order specialized imaging, such as a Magnetic Resonance Imaging (MRI) scan of the brain, to check for signs of a tumor, stroke, or structural damage from trauma. In cases where seizures are suspected, an Electroencephalogram (EEG) may be used to record the brain’s electrical activity and detect abnormal discharge patterns. Management of phantosmia depends on treating the identified cause, which could range from antibiotics for sinusitis to anticonvulsant medications for seizure disorders.