The sudden, distinct smell of gasoline when no source is present is a phenomenon that immediately draws attention and concern. This experience is a form of olfactory misperception, where the complex system responsible for our sense of smell mistakenly generates a signal. It is a biological event where the brain processes an odor despite the complete absence of odor molecules in the environment.
The Phenomenon of Phantosmia
The medical term for perceiving a smell that does not exist is phantosmia, which is technically classified as an olfactory hallucination. This occurs when the nerve cells or the brain’s processing centers malfunction, causing the sensation of smell without a corresponding external trigger. The olfactory receptors in the nose or the olfactory bulb may spontaneously fire, sending an erroneous signal to the cerebral cortex.
The perceived odor in phantosmia is often described as unpleasant, foul, burnt, or chemical, which is why the smell of gasoline is a frequent complaint. This tendency toward negative phantom smells is known as cacosmia. The phantom smell may be noticed in one nostril or both, and its characteristics can sometimes offer a clue about the underlying cause.
Common Non-Serious Triggers
Many cases of phantom smells originate in the nasal cavity and are considered non-serious, often resolving once the underlying condition clears. Issues affecting the nose and sinuses, such as chronic sinusitis or a severe upper respiratory infection, are among the most frequent causes. Inflammation and infection in the nasal passages can directly irritate the delicate olfactory nerves, causing them to send distorted signals to the brain.
Nasal polyps, which are non-cancerous growths, can also physically disrupt airflow and irritate the olfactory epithelium. Temporary damage to olfactory neurons following a severe cold or viral infection, including COVID-19, is known to sometimes manifest as phantosmia during the recovery phase. Certain medications can also temporarily alter the sense of smell, leading to phantom odors as a side effect.
Phantosmia may also manifest as an olfactory aura, a transient sensory symptom that precedes or accompanies a migraine episode. This temporary neurological event usually dissipates as the migraine resolves. If the phantom smell originates in the nose or is related to a temporary event like a migraine, the symptoms are often intermittent or may be stronger in one nostril than the other.
Serious Neurological Causes
When phantosmia is persistent and not linked to a nasal or sinus issue, it may point toward a central cause involving the brain’s olfactory pathways. The perception of an odor is ultimately processed in the temporal lobe, and disturbances in this area can generate the sensation of smell independently of input from the nose.
Temporal lobe seizures, often called simple partial seizures, are a serious neurological cause where an olfactory hallucination can be the initial symptom. During a seizure, abnormal electrical activity in the temporal lobe can trigger the distinct sensation of an odor like burning rubber or gasoline. These episodes are typically brief and may be accompanied by a feeling of déjà vu or other sensory changes.
Old head trauma can cause subtle damage to the olfactory bulb or neural connections, resulting in phantom smells years later. Though rare, a brain tumor or a stroke affecting smell perception regions can also manifest as phantosmia. In these central causes, the phantom smell is often more constant and equally noticeable in both nostrils, sometimes accompanied by other neurological symptoms like persistent headaches or changes in vision.
Diagnosis and Medical Evaluation
If the phantom smell of gasoline is persistent, worsening, or accompanied by other neurological symptoms, a medical evaluation is recommended. A doctor will typically begin by taking a comprehensive medical history, focusing on past head injuries, respiratory infections, and the specific characteristics of the phantom smell. The diagnostic process often involves a physical examination of the head and neck, including a thorough inspection of the nasal passages.
To investigate potential nasal causes, a healthcare provider might perform a nasal endoscopy, using a thin, lighted tube to visualize the nasal cavity and sinuses for signs of infection or polyps. If a central cause is suspected, the evaluation may include imaging studies. A computed tomography (CT) scan or magnetic resonance imaging (MRI) can help rule out structural abnormalities like tumors or evidence of a stroke affecting the olfactory pathway.
In some cases, an electroencephalogram (EEG) may be used to measure the brain’s electrical activity if a seizure disorder is suspected. The specialist, often an otolaryngologist or a neurologist, uses these test results to pinpoint the origin of the phantosmia. Identifying the cause is the necessary first step, as the appropriate management strategy depends entirely on the underlying condition.