Detecting an odor, such as perfume, in the quiet of the night when no physical source is present is a phenomenon that can be unsettling. This sensation is known scientifically as an olfactory hallucination, or phantosmia. It is a sensory event where your brain perceives a smell that is not actually in your environment. This internal signal indicates a disruption in the sense of smell. Understanding this experience involves looking at potential triggers in both the nasal passages and the central nervous system.
Defining Olfactory Hallucinations
Phantosmia is the medical term for perceiving an odor without an external odorant being present. While the smells are often described as unpleasant—such as burning rubber, smoke, or a chemical odor—a person can also experience pleasant scents, like perfume. The specific nature of the smell can vary greatly.
These phantom smells may be constant or they can come and go, sometimes affecting only one nostril. Phantosmia often becomes more noticeable in the middle of the night because the usual flood of daytime environmental stimuli is drastically reduced. With fewer external stimuli competing for attention, the brain may focus more intently on internal signals from the olfactory system.
Common Causes Related to the Nasal Passages
The most frequent sources of phantosmia are localized issues affecting the peripheral olfactory system, which includes the nose and nasal cavity. Conditions that cause inflammation in the nasal passages are common culprits, as they can irritate the delicate nerve endings responsible for smell detection. This irritation can cause the olfactory sensory neurons to fire off incorrect signals to the brain.
Chronic sinusitis or acute sinus infections are prime examples, where prolonged inflammation and swelling within the sinus cavities directly impact the olfactory region. Nasal polyps, which are soft, noncancerous growths, can similarly obstruct and inflame the area. Upper respiratory infections, such as a cold, the flu, or post-viral inflammation from an illness like COVID-19, are also commonly linked to temporary phantosmia. The phantom smell often resolves once the underlying infection or inflammation clears up.
Neurological Triggers and Central Nervous System Issues
When the phantom smell originates in the brain, it is classified as a central phantosmia, indicating a problem with how the brain processes or interprets smell signals. One recognized neurological cause is the olfactory aura associated with temporal lobe seizures. In this instance, the phantom smell is an electrical disturbance in the part of the brain that governs smell memory and processing, often serving as a warning sign that a seizure is about to occur.
Phantosmia can also manifest as part of a migraine aura, where the smell change precedes the onset of a headache. Physical trauma to the head, such as a concussion or severe blow, can damage the olfactory bulb or the neural pathways that transmit smell information, leading to persistent or recurring phantom smells. The sudden onset of an olfactory hallucination can, in rare cases, be a symptom of a more serious neurological condition, such as a brain lesion or tumor pressing on the olfactory cortex. These central nervous system causes affect the brain’s interpretation centers directly.
Determining When to Seek Medical Guidance
While many cases of phantosmia are benign and resolve on their own, especially when linked to a cold or sinus infection, some symptoms warrant a prompt consultation with a healthcare professional. If the phantom smell persists for more than a few weeks, seek medical advice to determine the underlying cause. A persistent phantom smell may require evaluation by an ear, nose, and throat (ENT) specialist or a neurologist.
Immediate medical guidance is recommended if the phantom smell is accompanied by other neurological symptoms. These red flags include vision changes, severe and persistent headaches, loss of consciousness, or noticeable motor function changes. If the smell is only perceived in one nostril, this can suggest a localized issue, such as a nasal polyp or lesion, which should be investigated. Early diagnosis of any underlying condition is important toward receiving appropriate treatment.