Smelling a strong, chemical odor like lighter fluid or gasoline when no source is present is a recognized medical phenomenon originating in the body’s complex olfactory system. This sensation, often described as unpleasant, burnt, or smoky, is a type of phantom smell known as an olfactory hallucination. It occurs when the nervous system responsible for smell perception misfires, generating a smell signal without an odor molecule. While unsettling, the symptom is frequently caused by common and treatable conditions, though it can also point to more significant underlying issues.
Defining Phantosmia and Parosmia
The experience of smelling something that is not there is called phantosmia, or phantom smell. This condition means the odor is perceived internally, without any external stimulus triggering the olfactory receptors. The smell is often described as foul, metallic, burnt toast, or a chemical; unpleasant odors are far more common than pleasant ones.
Phantosmia is often confused with parosmia, a distinct disorder involving a distorted sense of smell. With parosmia, a real odor is present, but the brain interprets it incorrectly. For example, a familiar scent like coffee or fruit might suddenly smell revolting, such as sewage or rotten food. Both conditions are classified as dysosmia, resulting from a malfunction along the olfactory pathway.
Olfactory System Irritations and Infections
Many cases of phantom smells originate in the nose and upper respiratory tract, where sensory nerves are irritated or damaged. These are often considered the most common causes of phantosmia. The lining of the nasal cavity contains millions of olfactory receptor neurons that can become inflamed or damaged by local issues.
One frequent culprit is chronic sinusitis, where persistent inflammation of the sinuses causes swelling and irritation that can lead to misfiring of the olfactory nerves. Upper respiratory infections, including the common cold, flu, and post-viral damage from infections like COVID-19, are also well-documented causes. When nerve endings sustain damage during a severe infection, healing and regeneration can lead to the nerve sending random, incorrect signals to the brain, which is interpreted as a strong odor.
Other structural issues within the nasal passages can also trigger phantom smells. Nasal polyps, which are soft, non-cancerous growths on the lining of the sinuses, and severe allergic rhinitis can obstruct airflow and cause chronic irritation to the sensitive olfactory epithelium. In these cases, the perceived chemical smell results from a peripheral malfunction, where the sensory cells in the nose generate the smell signal themselves.
Neurological Triggers and Conditions
When the cause of a phantom smell is not in the nasal passages, it can originate centrally within the brain, which processes the smell information. The brain can generate an olfactory signal without input from the nose, much like an electrical short circuit. These centrally originating phantom smells often present differently than those caused by infections, sometimes being sudden, fleeting, or occurring only in one nostril.
One significant neurological cause is temporal lobe epilepsy, where olfactory hallucinations can occur as an aura immediately preceding a seizure. The temporal lobe is the brain’s primary olfactory processing center, and abnormal electrical activity in this area can trigger the perception of a strong, unpleasant smell. Phantom odors can also be a symptom associated with migraine headaches, sometimes appearing as a sensory disturbance before the headache begins.
Sudden phantom smells can also be a symptom of structural issues in the brain, such as a lesion or a tumor located near the olfactory bulb or processing centers in the temporal lobe. Head trauma can damage the delicate olfactory pathways, leading to subsequent nerve misfiring and phantosmia. These central causes require specialized neurological investigation, as the phantom smell indicates a disruption in the brain’s ability to correctly interpret sensory input.
When to Seek Medical Consultation
While most cases of phantosmia are temporary and resolve on their own, especially those following a cold or flu, medical consultation is advised if the phantom smell persists for more than a few weeks without a clear, resolving cause. The persistence of the symptom indicates the underlying issue may not be a minor irritation.
It is important to seek prompt medical attention if the phantom smell is accompanied by other neurological symptoms. These red flags include the onset of seizures, severe or worsening headaches, changes in vision, unexplained confusion, or loss of balance. A smell occurring only on one side of the nose can also suggest a localized issue, like a polyp or obstruction, and should be checked.
The first step usually involves seeing a primary care physician, who may then refer you to specialists, such as an otolaryngologist (ENT), for an examination of the nasal passages. If a central cause is suspected, a referral to a neurologist will be necessary. These specialists can determine the root cause, which may involve a physical exam, a smell test, or imaging studies like a CT or MRI scan.