The experience of smelling food, like bacon, or an unpleasant odor, such as smoke, when no source is present is a phenomenon known as phantosmia, or an olfactory hallucination. The smells are often described as burnt, chemical, metallic, or foul. Phantosmia represents a malfunction within the complex system responsible for our sense of smell, and recognizing this symptom is the first step toward determining the underlying cause.
What Causes Phantom Smells
Phantosmia occurs when the olfactory system, the network responsible for detecting and interpreting odors, begins to generate signals on its own. The process can be classified as either peripheral, originating in the nose, or central, stemming from the brain. In a healthy system, odor molecules stimulate specialized receptor neurons high in the nasal cavity, which transmit electrical signals to the brain for interpretation. Phantosmia is frequently due to a misfiring of these olfactory neurons or an overstimulation that occurs without a real scent. This causes the brain to perceive an odor even though no chemical stimulus has been inhaled.
Nasal and Sinus Triggers
The most frequent and least concerning causes of phantosmia originate within the peripheral olfactory system, specifically the nasal and sinus passages. Inflammation or damage to the delicate olfactory epithelium can cause the receptor cells to spontaneously generate signals. Conditions like chronic sinusitis, allergic rhinitis, or nasal polyps can trigger these phantom smells by creating a constant state of irritation. Upper respiratory tract infections, including the common cold or recent viral illnesses like COVID-19, are known to damage the olfactory neurons, which can lead to phantosmia during the healing process. Dental issues, such as severe tooth decay or gum disease, may also be a contributing factor, as the inflammation can sometimes affect nearby nerves. When the phantosmia is peripheral, the phantom smell may sometimes be noticed more strongly in one nostril than the other. Exposure to certain environmental toxins or irritants, like heavy metals or tobacco smoke, can also damage the olfactory lining. Addressing the underlying inflammation, infection, or structural blockage in the nasal cavity often resolves the phantom smell.
Neurological Causes and Urgent Signs
When phantosmia is centrally driven, meaning the cause lies within the central nervous system, it can be a sign of a more serious condition. The smell of burning or smoke is frequently reported in these cases, and the perception is usually experienced equally in both nostrils. This specific type of olfactory hallucination is a recognized symptom of neurological events that affect the brain’s smell-processing centers, primarily located in the temporal lobe. A common neurological trigger is an olfactory aura, which can precede a focal seizure, particularly those originating in the temporal lobe. This aura is a brief, intense phantom smell that occurs just moments before the seizure activity begins. Head trauma, or a traumatic brain injury, can also disrupt the olfactory pathways, leading to chronic phantosmia. Other serious central nervous system causes include the presence of a brain tumor or the onset of a stroke, especially if the event impacts the olfactory bulb or the temporal lobe. If phantosmia is accompanied by additional symptoms, it warrants immediate medical evaluation. These urgent signs include persistent severe headaches, changes in vision, loss of consciousness, muscle weakness, or memory problems.
Medical Evaluation and Treatment
When phantom smells persist, a medical evaluation is required to determine the origin of the disorder. A primary care provider will typically begin with a thorough patient history and a physical examination of the head and neck. If a local nasal or sinus cause is suspected, the patient may be referred to an otolaryngologist, who can perform a nasal endoscopy to visually inspect the nasal passages and sinuses. If a central nervous system cause is considered, a referral to a neurologist will follow, often accompanied by diagnostic imaging. Imaging tests, such as a CT scan or MRI, are used to visualize the brain and rule out structural issues like tumors or signs of a stroke. Treatment for phantosmia is dependent on successfully managing the underlying cause. If the root problem is a sinus infection, antibiotics or anti-inflammatory drugs may resolve the phantom smell. For neurological causes, management might involve anti-seizure medications to stabilize brain activity. In rare cases of chronic phantosmia, certain medications or procedures may be used to temporarily block the olfactory receptors to provide relief.