Phantom smells, known medically as phantosmia, are most often a sign of something routine: a cold, sinus infection, allergies, or nasal polyps. About 6.5 percent of Americans over 40 experience phantom odors, and in a broader population-based study, roughly 4.2 percent of people reported olfactory hallucinations at some point. In less common cases, phantom smells can signal neurological conditions like migraines, seizures, or, rarely, brain tumors.
Common Causes: Infections and Nasal Issues
The most frequent triggers for phantom smells are upper respiratory problems. Colds, sinus infections, and allergies can all inflame or irritate the smell receptors high inside your nasal passages. When the tissue swells or gets coated in excess mucus, the signals sent to your brain can get scrambled, producing smells that aren’t there. People often describe these phantom odors as burnt, smoky, chemical, or rotten.
Nasal polyps, which are soft, noncancerous growths inside the sinuses, can also cause phantom smells, though this is less common than simply losing your sense of smell altogether. The key thing about all of these causes is that they’re temporary. Once the infection clears, the allergies are managed, or the polyps are treated, the phantom smells typically stop.
Rinsing your nasal passages with a saline solution or neti pot can help in the short term. Over-the-counter decongestant sprays may also reduce the congestion that’s contributing to the problem.
Migraines and Olfactory Auras
Some people smell things that aren’t there just before a migraine hits. This falls under the umbrella of migraine aura, a set of sensory disturbances that about 30 percent of migraine sufferers experience. Most auras are visual (flashing lights, zigzag lines), but they can also involve smell. You might notice a sudden, unexplained odor minutes before the headache begins.
The mechanism behind it is a wave of abnormal electrical activity that spreads across the brain’s surface, temporarily disrupting normal function. When that wave passes through areas involved in processing smell, it can generate phantom odors. These episodes are brief, usually resolving within an hour, and they follow a recognizable pattern tied to the migraine cycle. If you notice phantom smells repeatedly before headaches, that pattern itself is a useful clue for your doctor.
Temporal Lobe Seizures
A sudden, strange smell with no source can be a warning sign of a seizure originating in the temporal lobe, the part of the brain that sits behind your temples and plays a major role in processing smell and memory. These phantom odors act as what neurologists call an “aura,” a brief signal that a seizure is about to happen or is already underway. The smell is often described as unpleasant: burning rubber, chemicals, or something hard to name.
Temporal lobe seizures happen when a burst of abnormal electrical activity fires in that region. The seizure itself typically lasts 30 seconds to 2 minutes. During that time, a person may stare blankly, make repetitive movements, or be unable to respond to others. Not everyone with these seizures realizes they’re having them, especially if the episodes are subtle. Recurring phantom smells that come on suddenly, last briefly, and happen alongside confusion or a dreamlike feeling are worth investigating promptly.
Brain Tumors
Phantom smells are rarely caused by brain tumors, but this is the concern that drives many people to search. Tumors located near the olfactory system, particularly along the base of the skull where the smell nerves enter the brain, can produce olfactory hallucinations by putting pressure on those nerves. These are typically slow-growing tumors, and phantom smells would almost always appear alongside other symptoms: persistent headaches, vision changes, or personality shifts. An isolated phantom smell without any other neurological symptoms is very unlikely to be a tumor.
Anxiety, Depression, and Stress
Phantom smells aren’t limited to physical causes. Population-level research has found that self-reported anxiety symptoms and stressful life events are significantly associated with olfactory hallucinations. This doesn’t mean the smells are imagined in a dismissive sense. Stress and anxiety genuinely alter how the brain processes sensory information, and that can include generating smell perceptions without an external source.
In more severe psychiatric conditions like schizophrenia, olfactory hallucinations can occur alongside other types of hallucinations. But for most people experiencing phantom smells tied to stress or mood, the episodes tend to be occasional and resolve when the underlying mental health issue is addressed.
Phantosmia vs. Parosmia
It’s worth knowing the difference between two conditions that are easy to confuse. Phantosmia means smelling something when nothing is there at all. You’re sitting in a clean room and suddenly smell smoke or garbage. Parosmia, on the other hand, means a real smell gets distorted. Your morning coffee smells like sewage, or a flower smells like chemicals. Parosmia became widely recognized after COVID-19, when many people experienced distorted smells during recovery.
Both conditions involve the smell system misfiring, but they point to slightly different problems. Parosmia usually reflects damage to the smell receptors themselves (often from a viral infection), while phantosmia can originate either in the nose or in the brain. Knowing which one you’re dealing with helps narrow down the cause.
What the Smell Pattern Tells You
The timing, duration, and context of phantom smells offer important clues. Smells that showed up during or right after a cold and go away within a few weeks point to an inflammatory cause. Smells that flash for a few seconds and come with a strange sense of déjà vu or confusion suggest temporal lobe activity. Smells that build slowly before a pounding headache fit the migraine aura pattern.
Persistent phantom smells that don’t go away over weeks or months, especially if they’re accompanied by other neurological changes like memory problems, trouble finding words, or unexplained mood shifts, warrant a thorough evaluation. This typically involves imaging of the brain and sinuses, along with a detailed neurological exam. For the majority of people, though, phantom smells trace back to something treatable in the nose or sinuses, and they resolve once the underlying issue clears up.