The unsettling sensation of smelling smoke or a burning odor when no source is present is known as a phantom smell. This experience often raises concerns about serious neurological issues. While this symptom can be linked to conditions affecting the brain, it is far more often an indication of common, less threatening medical issues. This article provides clarity on the potential medical explanations for this sensation and outlines the necessary steps for proper evaluation.
Understanding Phantosmia: The Phantom Scent
Phantosmia is the technical term for perceiving an odor that is not physically present in the environment. This condition is a form of olfactory hallucination, meaning the sensation originates within the nervous system. The phantom scent experienced is usually unpleasant, often reported as the smell of smoke, burning rubber, metallic substances, or chemicals.
Phantosmia must be distinguished from parosmia, which involves a distorted perception of an existing smell. For example, a person with parosmia might smell a rose but perceive it as garbage. Phantosmia is characterized by smelling something completely absent. Although relatively uncommon, phantosmia makes up about 10 to 20 percent of all smell-related disorders.
The Specific Link to Brain Tumors and Seizures
The connection between phantom smoke and a brain tumor or seizure is rooted in the neurology of smell perception. Phantom smells originating in the brain are classified as central phantosmia. These olfactory hallucinations can sometimes be the first sign of a focal seizure, particularly those arising in the temporal lobe.
The temporal lobe contains the olfactory cortex, which processes smell signals. An abnormal surge of electrical activity in this region defines a seizure and can trigger the perception of an odor. When this occurs just before or as part of a seizure, it is known as an olfactory aura, often described as the smell of burning or smoke.
A mass, such as a tumor, located near the olfactory bulb or temporal lobe can irritate the surrounding brain tissue, leading to this electrical disturbance. While brain tumors are a potential cause, they are a rare cause of phantosmia. Other neurological conditions, such as mesial temporal sclerosis, are actually more frequent causes of these olfactory auras.
More Common Causes of Phantom Smells
While the neurological connection is significant, the majority of phantosmia cases are linked to common issues involving the nasal passages and peripheral nervous system. Problems in the nose or nasal cavity are the most frequent causes of these smell-related disorders. Estimates suggest that between 52 and 72 percent of conditions affecting the sense of smell are related to a sinus issue.
Sinonasal Issues
One of the most common causes is chronic sinonasal disease, such as severe sinus infections or chronic rhinitis, where inflammation affects the olfactory receptors. Nasal polyps, which are non-cancerous growths inside the nasal passages, can also interfere with the olfactory nerve pathway and trigger phantom smells.
Other Causes
Recent head injuries or trauma, including concussions, can temporarily or permanently disrupt the connection between the olfactory nerve and the brain. Phantom smells can also manifest as part of a migraine aura, preceding the onset of a headache. Dental issues, including gum disease, can also be a source of irritation that leads to phantosmia. Exposure to neurotoxins, such as lead or mercury, or certain medications have also been known to contribute to the experience of phantom smells.
Medical Evaluation and Next Steps
If you are experiencing phantom smells, the appropriate first step is to consult with a medical professional. A thorough medical history and physical examination will be performed to determine the onset, duration, and characteristics of the phantom smell. The initial evaluation focuses on ruling out the most common causes, starting with a comprehensive head and neck examination.
The doctor may refer you to an otolaryngologist, a specialist in ear, nose, and throat issues, who can perform a nasal endoscopy. This procedure uses a thin, flexible tube to visually inspect the nasal cavity and sinuses for conditions like polyps or signs of infection. If sinonasal pathology is suspected, a CT scan of the sinuses may be ordered.
If the initial workup does not reveal a nasal cause, the focus shifts to the central nervous system. A neurologist may order an MRI of the brain to look for structural abnormalities, such as a tumor or stroke. An electroencephalogram (EEG), which measures the brain’s electrical activity, may also be necessary if seizure activity is suspected.