Experiencing the perception of smoke, either by smell or sight, when no source exists can be unsettling. This phantom sensation, often mimicking the odor of burning rubber or wood smoke, represents a disconnect between the senses and the external environment. Understanding these perceptions involves examining how the olfactory and visual pathways process information and how disruptions lead to hallucinations. This phenomenon can arise from issues localized in the sensory organs or from complex origins within the brain’s central processing centers.
Defining Phantosmia
The medical term for smelling an odor that is not actually present is phantosmia, or an olfactory hallucination. This condition is a qualitative olfactory disorder, meaning the perception of the smell is distorted, unlike anosmia (loss of smell) or hyposmia (diminished smell). The sensation can occur in one or both nostrils and may be intermittent or persistent.
Most people with phantosmia report perceiving an unpleasant odor, known as cacosmia. The most common phantom smells are associated with burning, such as burnt toast, cigarette smoke, or rubber. Phantosmia is distinct from parosmia, where an actual odor is present but perceived incorrectly (e.g., coffee smelling like garbage). The phantom smell is generated internally, either from malfunctioning olfactory neurons or aberrant central integration in the brain.
Central Nervous System Causes
When a phantom smell originates in the brain, it is classified as central phantosmia. A serious neurological cause is focal seizures, particularly those originating in the temporal lobe, which handles olfactory processing. An olfactory hallucination can act as an aura, or warning sign, preceding a full seizure event. Patients with temporal lobe lesions caused by a stroke, head trauma, or a brain tumor may also experience these hallucinations.
Another neurological trigger is the migraine aura, where sensory disturbances precede or accompany a headache episode. While visual auras are more common, some people experience an olfactory aura, which may include the smell of smoke or foul odors. These phantom odors occur because of the spontaneous or incorrect firing of neurons in the brain centers that process smell. Any sudden, persistent, or recurring episode of phantom smell, especially with neurological symptoms like confusion or weakness, warrants immediate medical evaluation.
Peripheral Olfactory System Causes
Phantosmia can also arise from issues in the nasal cavity or the olfactory epithelium, the tissue containing the sensory receptors for smell. This is known as peripheral phantosmia, where the olfactory neurons malfunction and send incorrect signals to the brain. Common conditions like chronic sinusitis or nasal infections cause inflammation that can damage or irritate these receptors.
Physical obstructions, such as nasal polyps or tumors, can interfere with the olfactory system’s normal function. Viruses, including those causing the common cold or COVID-19, can temporarily or permanently injure olfactory neurons, leading to phantosmia. Severe dental problems or abscesses can also trigger phantom odors due to their proximity to the olfactory bulb. These peripheral causes are localized and often resolve once the underlying issue is successfully treated.
Visual Phenomena That Mimic Smoke
While perceiving smoke is usually an olfactory hallucination, “seeing smoke” refers to a hazy or cloud-like visual disturbance. The most frequent cause is vitreous floaters, which are small clumps of fibers or cells within the eye’s vitreous humor. As light enters, these floaters cast shadows onto the retina, interpreted by the brain as specks, strands, or wisps resembling smoke.
A sudden shower of new floaters, especially with flashes of light, indicates that the vitreous gel is pulling away from the retina. This event, posterior vitreous detachment, can cause a retinal tear. A retinal tear is a medical emergency requiring immediate attention to prevent permanent vision loss.
Other ocular conditions, such as cataracts, cause the lens to become cloudy. This results in a gradual blurring or haziness of vision that a person might interpret as a constant smoky veil.
A more complex visual cause is Charles Bonnet Syndrome (CBS), which involves visual hallucinations in people with significant vision loss. The brain, receiving less input, spontaneously generates images ranging from simple geometric patterns to complex scenes. Although CBS hallucinations are exclusively visual and distinct from phantosmia, the underlying visual impairment often involves persistent cloudy or hazy vision.