Smell is the sense people pay the least attention to until something goes wrong with it. Olfactory hallucinations — perceiving smells with no source — are one of the less common forms of hallucination in schizophrenia, but they have a wide differential diagnosis and are worth understanding clearly. Many of the conditions that cause them are not psychiatric at all, which is why a careful evaluation matters whenever they appear.
Olfactory hallucinations are perceptions of smell with no external source, occur in a minority of people with schizophrenia, and almost always need evaluation for medical and neurological causes alongside the psychiatric one.
What people smell
Reports cluster around unpleasant odours far more often than pleasant ones. Common descriptions include burning, smoke, rot, decay, sewage, gas, faeces, bleach, and chemical or metallic smells. A minority of people report pleasant smells — flowers, perfume, food. The hallucinated smell may be constant, intermittent, or tied to specific places or times of day.
Two related terms are worth knowing:
- Phantosmia — smelling something that isn't there at all.
- Parosmia — a real smell perceived as something different (often unpleasant). Parosmia became more widely known after COVID-19.
Olfactory hallucinations in psychiatric contexts are usually phantosmia.
How common in schizophrenia
Estimates from clinical samples place the prevalence of olfactory hallucinations in schizophrenia at roughly 5–15%. They tend to occur alongside other hallucinations and delusions rather than alone. When they appear in isolation, the chance of a non-psychiatric cause rises.
The differential diagnosis
The list of conditions that can produce phantom smells is long and worth taking seriously:
- Temporal lobe epilepsy. The classic example. A brief, stereotyped smell preceding a seizure is a known aura. Any new olfactory hallucination warrants neurological consideration.
- Migraine. Olfactory aura, though less common than visual aura, is well described.
- Sinus disease and nasal polyps. Local irritation can generate phantom smells.
- Head injury. Damage to the olfactory bulb or temporal cortex can produce them.
- Brain tumours. Particularly meningiomas of the olfactory groove.
- Parkinson's disease and Lewy body dementia. Olfactory dysfunction is an early feature.
- Post-viral changes. COVID-19 has dramatically increased the prevalence of parosmia and phantosmia.
- Medication side effects. Several drug classes can produce phantom smells.
- Substance use. Cocaine and amphetamine in particular.
- Schizophrenia and other primary psychotic disorders.
The point of the list is not to alarm but to underline that smelling something that isn't there is rarely treated as solely a psychiatric symptom on a first presentation.
How they are evaluated
A clinician usually asks about onset, content, duration, accompanying symptoms (especially seizure-like episodes, headache, vision change, weakness), recent infections, head injury, substance use, and other psychotic symptoms. A neurological exam is standard. Brain imaging and EEG are commonly considered, particularly when the hallucination is new, brief and stereotyped, or accompanied by other neurological signs.
Phantom smells appear suddenly, are brief and stereotyped (the same odour, in the same way, repeated), follow a head injury, or come with confusion, loss of awareness, headache, or vision changes. These features can point to seizure or another neurological cause that needs urgent evaluation.
Treatment
Treatment depends on cause. When the olfactory hallucinations are part of schizophrenia, the standard antipsychotic approach often helps. When they are part of epilepsy, anticonvulsants are first-line. When they are caused by a sinus problem, an ENT referral may resolve them. When they are post-viral, time and olfactory training are the mainstays. The point is that "olfactory hallucination" is a presentation, not a diagnosis.
Living with olfactory hallucinations
People who experience them in the context of schizophrenia describe a few things consistently. The smells are often perceived as evidence of something real — gas leaks, decay in the apartment, contamination — and they can drive intensive checking behaviours or reinforce delusional explanations. A trusted friend or family member who can do the reality-testing ("I checked the kitchen, there's no gas") often reduces the practical disruption.
Practical coping tools include:
- Adding strong real smells to a room — coffee, citrus, essential oils — to compete with the phantom one.
- Tracking patterns. Some people notice clusters at specific times of day or after specific stressors.
- Avoiding stimulants and substances that can amplify the experience.
- Improving sleep, which reduces hallucination intensity across modalities.
Why this matters
Olfactory hallucinations are less talked about than voices, but they affect functioning in distinct ways — they can drive eating problems, fixation on contamination, and significant social embarrassment. They also deserve careful workup because their differential includes treatable conditions. The right answer to a new phantom smell is usually a conversation with a clinician, not a guess.
This article is for educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a qualified mental health professional. If you or someone you know is in crisis, call or text 988 in the US, or your local emergency number.