When a person detects the odor of wood smoke, burning rubber, or chemical fumes without any physical source, they are experiencing a condition called phantosmia. This phenomenon is the perception of a smell that is not actually present in the environment. The experience can be unsettling, especially when the phantom smell is unpleasant, like smoke, which is one of the most commonly reported phantom odors. Understanding why this happens requires looking into the system responsible for our sense of smell, which can malfunction either at the peripheral level, in the nose and sinuses, or at the central level, within the brain itself.
What Is Phantosmia?
Phantosmia is the medical term for a phantom odor perception, resulting from a malfunction in the olfactory system that causes the brain to interpret a signal as a smell. The olfactory system, which processes scent, can generate this false signal when its delicate nerve pathways are disrupted. This misfiring creates the illusion of an odor even though no scent molecules are stimulating the nose. Most people who experience phantosmia report that the smells are disagreeable, often described as burnt, foul, or chemical-like. This perception of an unpleasant phantom odor is sometimes referred to as cacosmia. The experience is usually intermittent, but when it persists, it can significantly affect a person’s appetite and overall quality of life.
Causes Originating in the Nasal Cavity and Olfactory Epithelium
Many cases of phantosmia originate in the peripheral olfactory system, which includes the nostrils, nasal cavity, and the specialized tissue lining it. This tissue, called the olfactory epithelium, contains the sensory neurons responsible for detecting odors. Inflammation or damage in this region can cause the neurons to misfire, sending distorted signals to the brain that are misinterpreted as a smell.
Conditions such as chronic sinusitis, severe colds, or other upper respiratory tract infections are frequent causes of this peripheral disruption. The swelling and inflammation associated with these illnesses can irritate the olfactory nerves, leading to the spontaneous generation of a phantom scent. Nasal polyps, which are soft, noncancerous growths in the nasal passages or sinuses, can also physically interfere with the normal function of the olfactory pathways. When the phantom smell is due to a local problem like this, it may sometimes be perceived in only one nostril.
Central Nervous System Triggers
When the cause of a phantom smell is not in the nose, the source is likely located in the central nervous system, involving the brain’s processing centers for smell. The olfactory bulb and the temporal lobe of the brain are involved in translating and integrating odor signals, and aberrant electrical activity in these areas can generate a phantosmia. Temporal lobe seizures, which are a form of focal seizure, are a well-documented cause.
In these cases, the phantom smell, often described as burnt rubber or cigarette smoke, acts as an olfactory aura that precedes or accompanies the seizure event. This experience can be short-lived, lasting only a few seconds or minutes. The perception of a phantom smell can also be linked to other neurological events, such as migraines. The phantom odor may occur as part of the migraine aura, a sensory disturbance that occurs before the headache phase.
A traumatic brain injury can damage the delicate pathways that connect the nose to the brain’s processing centers, leading to a persistent or intermittent phantom smell. In rare instances, a tumor affecting the olfactory bulb or the temporal lobe can cause phantosmia by directly irritating the nerve tissue responsible for smell processing. In these central cases, the brain is creating the sensation internally due to an electrical or structural abnormality.
When to Consult a Healthcare Professional
While phantosmia can often resolve on its own, especially when linked to a temporary infection, persistent or sudden phantom smells warrant professional evaluation. You should consult a healthcare provider if the phantom smell lasts longer than a few weeks or if it is accompanied by other neurological symptoms. The sudden onset of a phantom smell, particularly if it is intense and only in one nostril, may suggest a more serious underlying issue.
Accompanying symptoms that signal a potential central nervous system trigger include:
- Persistent or severe headaches
- Visual disturbances
- Memory changes
- Seizure-like activity
The diagnostic process typically begins with a primary care provider who may then refer you to an otolaryngologist (ENT specialist) to rule out nasal or sinus conditions. If a neurological cause is suspected, a neurologist may order imaging tests like a CT scan or MRI to examine the brain, or an electroencephalogram (EEG) to check for abnormal electrical activity.