Olfactory hallucinations

1. Overview — What are Olfactory hallucinations?

Olfactory hallucinations, often called Phantosmia, are a condition in which a person
“smells something even though, in the real physical environment, there is no actual source of that smell at all.”

The patient feels that

“the smell is very strong, as if it were really right nearby.”

But when other people try to smell it, or when they check for a source (for example checking the house, the room, the gas stove),

they “cannot find any identifiable source of the odor” at all.

This condition belongs to the group of hallucinations (perceptual hallucinations) but happens specifically in the “olfactory system”, so it is usually called an olfactory hallucination or phantom smell.

The word hallucination literally means “a perception in the absence of an external stimulus.”
Therefore, an olfactory hallucination is a perception of smell generated by the brain, not by actual chemical molecules in the air.

The important point is:

It is not just “overthinking” or “vaguely feeling a faint smell” with uncertainty.

In many cases, the person is very certain that there is really a smell there. The experience feels just like smelling a real odor.

Some people will even get up and check the entire house, check the gas stove, check the electrical wiring, because they are convinced there is a burning smell or a gas leak.

The smells commonly reported in olfactory hallucinations are usually unpleasant odors, such as:

The smell of burning, burning rubber, or burning electrical wires

The smell of cigarette smoke, even though no one is smoking in the room

The smell of rot, corpses, sewage, or decomposing organic matter

Strange chemical odors, medicine-like smells, or cleaning products such as toilet cleaner, etc.

However, there are some cases reporting that they smell things like:

Perfume, the scent of flowers, or food smells

The odor may be “familiar” or something they have “never encountered in real life before.”

What makes olfactory hallucinations both clinically fascinating and clinically troublesome is that:

They are not limited to purely psychiatric diseases.

We can find phantom smells in:

ENT (ear–nose–throat) conditions, such as chronic nasal cavity inflammation, sinusitis, or infections following colds/viral illnesses

Neurological diseases, such as temporal lobe epilepsy, brain tumors, Parkinson’s disease, or certain types of dementia

Psychiatric illnesses, such as the schizophrenia spectrum, bipolar disorder with psychotic features, and major depressive disorder with psychotic features

In some cases, phantom smells are one of the earliest warning signs that there may be something wrong in the brain.

For example, in temporal lobe epilepsy, some patients experience a “brief, sudden olfactory hallucination” as a kind of warning signal (aura) before a seizure occurs.

In certain cases of brain tumors or other neurodegenerative diseases, phantom smells can appear as a prodromal symptom before other symptoms become obvious.

In the context of psychiatric disorders:

An olfactory hallucination may “match the theme” of the person’s delusional content.

For example:

A person who believes that their body is decomposing or dead may constantly smell the odor of a rotting corpse coming from themselves.

Someone who believes that others are trying to poison them may smell strange chemical or medicinal odors in the food they eat.

For some patients, phantom smells cause severe distress.

They may want to shut the door, isolate themselves, and be afraid to go outside.

Some have difficulty eating because they smell something disgusting all the time.

Some begin to think they are “going crazy,” because others don’t believe or don’t understand that they are truly smelling something.

Important: Olfactory hallucinations must be distinguished from other smell-related conditions, such as:

Anosmia – complete loss of smell

Hyposmia – reduced ability to smell

Parosmia – there is a real smell, but the brain “misinterprets” it; for example, the smell of coffee becomes the smell of garbage, or perfume becomes the smell of burning

Olfactory Reference Syndrome (ORS) – the patient has a fixed belief that they have terrible body odor or bad breath that disgusts others, even though no one else can smell it (the core here is a “belief” rather than a true olfactory hallucination like phantosmia)

Finally, what should be emphasized to general readers is:

Having olfactory hallucinations does not automatically mean the person is psychotic or “insane.”

Rather, it is a signal that the olfactory system, the brain, or the nose may have something wrong.

If the symptom recurs repeatedly, becomes chronic, or is severe enough to disrupt daily life, the person should see a doctor (ENT specialist, neurologist, or psychiatrist) to find the real cause.

If we were to summarize as briefly as possible for a highlight box on a website:

“Olfactory hallucinations = the brain creates a smell by itself, even though in the real world there are no actual chemical molecules of that smell present.”

2. Core Symptoms — Main symptoms of Olfactory hallucinations (Phantosmia)

This section explains “what patients actually experience” when they say they have phantom smells: what it looks like, how it feels, what patterns it follows, and how it impacts their life.

2.1) Smelling something that does not exist (phantom smells)

This is the central core of olfactory hallucinations.

Patients may say things like:

“It’s like there’s a really strong burning smell, but I can’t find the source at all.”

“I smell cigarette smoke all day, even though no one smokes in the house.”

“Out of nowhere I smell something extremely rotten, even though the room is clean.”

Their experience is not like a brief “whiff” where they doubt themselves and think, “Maybe I imagined it.” Instead, it has the characteristics of:

A strong, clear odor

High certainty

A sense that there is a “source” nearby (they just can’t find it)

The key point is that the smell does not come from a real stimulus.

The room, the house, and the workplace can be checked thoroughly, and nothing abnormal is found.

People around them try to smell and say: “There’s no smell at all.”

Clinically, we therefore regard this as a hallucination (the brain creating a perception on its own), not merely “being more sensitive to smell than others” or simply “having a very sharp nose.”

2.2) The character of the smell (quality of the odor)

Overall, the odor is usually unpleasant or disgusting.

Common examples include:

Burning smells / scorching rubber / burning electrical wires

Cigarette smoke, smoke from fire, pollution

Rotting smells, corpse-like odors, spoiled or putrid organic smells

Chemical odors, medicines, disinfectants, or bathroom cleaning products

What we often see is:

Patients use words like “really disgusting,” “unbearable,” or “feels dirty/repulsive” to describe the smell.

This leads to avoidance behaviors, such as leaving the room, changing where they live, or avoiding certain foods.

However, not every case involves a bad smell.

Some people report:

The smell of perfume, baby powder, flowers, or favorite foods, even though there is nothing in the room.

Some say it is “a strange odor they have never smelled in their entire life,” as if the brain invented a completely new smell by itself.

In summary:
Most phantom smells in phantosmia are unpleasant and distressing, but they can also be neutral or pleasant odors. The crucial point is that the odor should not exist in that situation, yet the brain still perceives it as if it were really there.

2.3) Time course and pattern of symptoms

This part is very important, because the temporal pattern can tell us a lot about the underlying cause.

Episodic / brief pattern

The smell comes and goes, each episode lasting only a few seconds to a few minutes.

This pattern is often seen in:

Temporal lobe epilepsy – olfactory aura before a seizure.

Example: suddenly smelling a strong burning rubber smell for 10–20 seconds → followed by feeling strange/deja vu/confused → then going into a seizure.

After the episode passes, the smell disappears completely as if nothing happened.

Persistent / chronic pattern

The phantom smell persists for hours, all day, or stretches over weeks to months.

This pattern is often seen in:

Post-viral smell disorder (after a cold, COVID-19, etc.)
Nasal cavity/sinus diseases
Psychiatric illnesses that include psychotic symptoms

Patients may say things like:

“All day I smell something disgusting, like I’m living in a pile of garbage.”
“I wake up smelling it, and I still smell it when I go to bed.”

Trigger-based pattern

Some people notice that phantom smells become stronger in certain situations, such as:

Being alone in a quiet room

Just before sleep / just after waking up

During periods of high stress

This pattern may be related to a mix of ENT issues, neural hyperexcitability, or anxiety/psychosis.

2.4) Laterality — one-sided or both-sided smell?

This helps differentiate between problems in the nose/sinuses and problems in the brain.

Peripheral / ENT-related (e.g., sinusitis, nasal polyps)

It is often reported that the bad smell is much more prominent on one side than the other.

For example: “It’s like there’s a decaying smell coming from my right nostril.”

Other symptoms may accompany it, such as nasal congestion, runny nose, or sinus pain.

Central / brain-related

Patients often describe:

The smell “floating up from inside the head,”

Or “coming through both nostrils at the same time.”

They do not feel that “one nostril is especially abnormal.”

This pattern is often associated with brain conditions such as epilepsy, tumors, neurodegenerative diseases, or psychotic disorders.

Summary for website writing:

If phantom smells + nasal congestion/sinusitis + a clear bad smell from one nostril → suggests an ENT/peripheral cause.

If phantom smells clearly feel like they are “coming from inside the head,” with no nasal symptoms but with seizures/deja vu/other neurological signs → suggests a neurological/psychiatric cause.

2.5) Emotional dimension and impact on daily life

Olfactory hallucinations are not just about a “strange nose.” They can hit emotions and quality of life very hard.

Common emotional effects:

Anxiety and fear

Fear that the house is actually on fire.
Fear that there is a gas leak they cannot detect.
Fear that they themselves smell terrible and others are disgusted.

A sense of being out of sync with reality (derealization-like)

Because what they perceive “does not match” what everyone else says.
Some start to wonder, “Am I going crazy?”

Behavioral changes:

Checking gas stoves, power outlets, and plugs repeatedly multiple times a day.

Keeping windows/fans open all the time, avoiding closed spaces.

Stopping eating out or avoiding social situations because of fear of smells (both their own perceived odor and the phantom smells).

Long-term effects:

Poor sleep quality (insomnia due to unpleasant smells or fear of accidents).

Depression and hopelessness (feeling that “living with this kind of smell all day makes life extremely difficult”).

Strained relationships with others (because others may see it as “overthinking” or “no big deal”).

2.6) Prevalence and co-occurring hallucination modalities

Some population-based studies report that:

Approximately 4% of the population have experienced olfactory hallucinations at least once in their life.

And in this group, more than half also have other hallucination modalities, such as:

Hearing voices (auditory hallucinations)
Seeing things that are not there (visual hallucinations)

Which means:

For some people, olfactory hallucinations are part of a broader psychotic picture.

But for many others, they are an isolated symptom linked to nasal/sinus diseases or neurological conditions.

3. Diagnostic Criteria — What is used to diagnose Olfactory hallucinations?

This section is not about criteria for a disorder called “Olfactory Hallucination Disorder,” because DSM-5-TR does not have a diagnosis with that name.
What we do have is:

The concept of hallucinations as a symptom,

Then we specify the modality as olfactory.

So in psychiatry and neurology, we usually diagnose in forms like:

Schizophrenia with olfactory hallucinations

Bipolar I disorder, current episode manic, with psychotic features, with olfactory hallucinations

Temporal lobe epilepsy with olfactory aura

Post-viral phantosmia

etc.

When you write the Diagnostic Criteria section on your website, it should focus on:

“How do we decide whether the symptoms a patient reports qualify as an ‘olfactory hallucination’ and in which diagnostic framework that symptom belongs?”

3.1) Principles from the definition of hallucination in DSM-5/DSM-5-TR

Even though there is no specific set of criteria for olfactory hallucinations, DSM provides a broad framework for “hallucinations” that we can apply:

There is a perception-like experience

In this context, “a smell.”
The quality of the smell is close to that of a real odor (clear, straightforward, not just a casual thought).

It occurs when there is no external stimulus.

The environment is checked and no source of the odor can be found.
It is not simply “having a better sense of smell” than others (not just hyperosmia).

The vividness and sense of reality are high.

The patient feels “it’s real” to the point that they get up to check the environment.
It is not just a faint imagined smell floating in their mind.

It does not occur exclusively during sleep, dreams, or transitional states (hypnagogic/hypnopompic).

If it happens only when falling asleep or waking up, it might be considered a semi-dream, semi-normal experience.
But if it occurs in broad daylight, while fully awake and alert, it fits the concept of hallucination more clearly.

It cannot be fully explained by the effects of substances/medications or by a purely medical condition alone.

For example, intoxication from drugs, medications, or metabolic delirium, etc.
In practice, however, clinicians always have to look for physical causes first before jumping to psychotic disorders.

3.2) Clinical reasoning structure — how diagnosis actually works in practice

In real life, diagnosing olfactory hallucinations often proceeds as follows:

Step 1: First confirm that “this is truly a hallucination.”

Ask and examine to distinguish:

Is there a real source?

Is there hidden garbage in the room? Is someone smoking and the patient doesn’t know? Is there a real gas leak?

Is it a misinterpretation of a real smell (parosmia)?

There is a real odor, but the patient perceives it as something distorted (e.g., coffee smells rotten) = parosmia.
If there is no stimulus at all, but the person smells something → phantosmia/hallucination.

Is it a false belief (delusion) instead (Olfactory Reference Syndrome)?

In ORS, the person believes they smell terrible and that others are disgusted.
But they do not necessarily “smell it themselves,” and the smell is not the starting point of the experience. The core is the belief that they have a bad odor.

If we can rule out a real stimulus + parosmia + ORS, then we categorize it as an olfactory hallucination.

Step 2: Identify the “diagnostic framework” that this symptom belongs to

3.2.1 ENT / Peripheral causes

Questions/signs clinicians look for:

Did symptoms start after a respiratory infection / COVID / nasal surgery?

Is there chronic nasal congestion, persistent runny nose, sinus pain, or unilateral nasal blockage?

Is the foul odor clearly coming from one nostril only?

If yes → we lean toward post-viral phantosmia, chronic sinusitis, nasal polyps, etc.

Diagnostic tools:

Nasal endoscopy

CT scan of the sinuses

ENT examination

3.2.2 Neurological causes

Look for neurological “red flags”:

Are there seizures, or do they feel a strange aura (deja vu, visual phenomena, confusion)?

Any numbness or weakness in some body part, slurred speech, blurred vision, or other focal brain signs?

Any history of head trauma, tumors, stroke, Parkinson’s disease, or dementia?

If suspicious → proceed with:

MRI brain / CT brain

EEG (if epilepsy is suspected)

Then diagnose conditions like:

Temporal lobe epilepsy with olfactory aura

Brain tumor with olfactory hallucinations

Neurodegenerative disease with olfactory dysfunction

3.2.3 Psychiatric / Psychotic causes

Assess whether there is a broader schizophrenia/psychotic syndrome:

Are there delusions? (e.g., beliefs about being poisoned, being persecuted, being dead)

Are there other hallucination modalities? (hearing voices insulting/commanding, visual hallucinations)

Is there disorganized speech or negative symptoms? (incoherent speech, answering off-topic, social withdrawal, flat affect)

Are there strong mood changes (mania/depression)?

If yes → we embed the olfactory hallucinations into a larger diagnosis, such as:

Schizophrenia with auditory, visual, and olfactory hallucinations

Schizoaffective disorder

Bipolar I disorder, current episode manic, with psychotic features and olfactory hallucinations

Major depressive disorder with psychotic features

3.3) “Minimum” criteria for when a symptom counts as an Olfactory hallucination

You can turn this into bullet points on your website:

We consider a symptom to meet criteria for olfactory hallucination if:

The patient clearly reports “smelling” something, even though:

The real environment has no detectable source of that smell.
Other people in the same environment do not smell it at all.

The subjective experience of the smell has high realism:

It is as clear as a real odor.
It prompts the person to act (e.g., get up to check the gas stove, open windows, etc.).

The episode happens while awake and conscious, not just during sleep or dreamlike states (not only when falling asleep or just waking).

Reasonable checks reveal no obvious simple source:

No actual odor source in the environment
Not merely severe dental/mouth odor or another clear physical smell source in the home

If there are physical/medication/substance factors present, clinicians must evaluate whether:

The phantom smell goes beyond what would be expected from that condition alone.
If it can be fully explained by delirium, intoxication, or withdrawal → it should be classified within that framework.

3.4) Where DSM mentions tactile/olfactory hallucinations in Delusional Disorder (for added depth on your website)

DSM includes a note that:

In Delusional Disorder, the main criterion is the presence of delusions (false, fixed beliefs).

However, tactile or olfactory hallucinations can occur as well,

Provided that:

They match the theme of the delusion, and
They are not prominent enough to reclassify the condition as another psychotic disorder such as schizophrenia.

Examples you can use in writing:

A person with the delusion that they are being “poisoned with toxic gas” may smell chemicals/gas even when none is there.

A person with the delusion that their body is rotting may constantly smell the odor of decay from themselves.

This helps your website show readers that:

Sometimes olfactory hallucinations are just “accompanying symptoms” that support an existing delusional theme.

Other times, they are “core symptoms” of a neurological or post-viral condition with no delusions at all.

3.5) Summary structure of Diagnostic Criteria for website use

You can summarize this section on Nerdyssey in a single clean framework (which you can then polish), for example:

Definition:

Olfactory hallucinations = smelling odors in the absence of any real stimulus in the environment.

Key characteristics:

The smell feels realistic and vivid.

It occurs while the person is awake and conscious.

It is not just imagining a smell or recalling it mentally.

Differential diagnosis (distinguishing from other conditions):

Differentiate from parosmia (there is a real stimulus, but perception is distorted).

Differentiate from ORS (a belief of being malodorous, not a true phantom smell per se).

Differentiate from real environmental odors.

Finding the diagnostic framework:

ENT: sinusitis, post-viral, post-COVID phantosmia, etc.

Neurology: temporal lobe epilepsy, brain tumor, stroke, neurodegeneration.

Psychiatry: schizophrenia spectrum, mood disorders with psychotic features, delusional disorder.

Real-world diagnosis in clinical practice:

We do not use a label like “olfactory hallucination disorder.”

Instead, we list this symptom as part of a broader diagnosis, such as:

Schizophrenia with olfactory hallucinations
Temporal lobe epilepsy with olfactory aura
Post-viral phantosmia, etc.

4. Subtypes or Specifiers — Forms / practical sub-classification

In theory, there is no official “subtype” classification. But in clinical work, we often divide olfactory hallucinations in practical ways to help with differential diagnosis:

4.1) Based on neurological origin

Peripheral / ENT-related phantosmia NCBI+1

Problems in the nose/sinuses/nasal cavity, such as post-viral olfactory dysfunction, chronic sinusitis, nasal polyps.

Often unilateral, worse when lying down or in quiet environments, sometimes with strong episodic smells.

Central (brain-related) olfactory hallucinations

Involving the temporal lobe, orbitofrontal cortex, and limbic system.

Seen in epilepsy, brain tumors, stroke, Parkinson’s disease, Alzheimer’s disease, schizophrenia, etc. PMC+2Cureus+2

Often persistent or appear as an aura before a seizure.

4.2) Based on duration

Episodic / brief – only a few seconds to a few minutes, such as olfactory aura before seizures.

Persistent / chronic – daily or lasting for weeks–months; often associated with post-viral states, chronic rhinosinusitis, or comorbid psychiatric conditions. NCBI+1

4.3) Based on psychiatric context

Psychotic olfactory hallucinations

Occur as part of a psychotic syndrome (delusions, disorganized thought, negative symptoms, etc.).

Found in schizophrenia, schizoaffective disorder, bipolar disorder with psychotic features, severe depression with psychosis. Psychiatrist.com+1

Non-psychotic / anxiety-related olfactory hallucinations

Case reports in some anxiety disorders where olfactory hallucinations occur in isolation, without other psychotic symptoms. Frontiers

4.4) Distinguishing from “Olfactory Reference Syndrome (ORS)” (very important)

ORS = a fixed belief that one has terrible body odor or bad breath that repulses others, even though no one else can smell anything.

The core is a “belief/delusion about one’s own smell,” not “experiencing strange smells” per se.

Some cases may have olfactory hallucinations as well, but in most, it is a mixture of misinterpreting others’ reactions and a delusional belief. PMC+2Wikipedia+2

5. Brain & Neurobiology — Neural mechanisms involved in Olfactory hallucinations

The olfactory system is a sensory system that is more “primitive” and “raw” than other senses because it connects directly to the limbic system (emotion + memory), with minimal filtering through the thalamus compared to vision or hearing. This explains why smells are often tightly bound to memories and emotions, and why, when these circuits go wrong, phantom smells (phantosmia) can arise quite easily.

5.1) A brief map of the olfactory pathway — from nose to brain

The main structures involved in olfactory hallucinations include:

Olfactory epithelium

Located at the top of the nasal cavity, containing receptor neurons sensitive to odor molecules.

If these receptor cells are damaged (post-viral, chemical exposure, trauma), the signals sent to the brain become “distorted” or patchy → the brain may respond by “filling in” smells on its own (phantom smells).

Olfactory nerve & olfactory bulb

The first relay station where smell signals from the nose enter the brain.

The olfactory bulb acts like a “hub” that organizes signals before sending them to deeper structures.

Abnormalities in the olfactory bulb (e.g., inflammation/degeneration) have been found in conditions like Parkinson’s disease, Alzheimer’s disease, and post-viral smell disorders, which are associated with phantosmia/anosmia/parosmia.

Primary olfactory cortex (piriform cortex, entorhinal cortex)

Responsible for the basic perception of “there is a smell.”

This is where patterns of odors start to be separated and recognized.

Hyperexcitability in this region can make the brain perceive smells on its own without any external stimulus.

Amygdala and other limbic structures

Link smells with emotions, such as fear, disgust, relaxation, nostalgia, etc.

When an olfactory hallucination is accompanied by intense fear or paranoia (e.g., the smell of burning, decay), it often reflects dysfunction along the olfactory–limbic pathway.

Orbitofrontal cortex (OFC)

A high-order olfactory area.

Helps interpret what the smell is and whether it is liked/disliked or good/bad.

Distortions in the OFC–limbic network may cause noise from the olfactory cortex to be interpreted as a “real smell” and emotionally labeled (e.g., “this is the smell of a fire” → triggers fear).

Temporal lobe networks, especially the medial temporal lobe

Involved in episodic memory, complex sensory integration, and various “experiential phenomena.”

In temporal lobe epilepsy (TLE), neurons in regions such as the hippocampus, amygdala, parahippocampal gyrus, and piriform cortex fire abnormally.

This abnormal firing can manifest as an olfactory aura—a sudden phantom smell before a seizure (e.g., burning, rot, rubber).

5.2) Why does the brain “create smells by itself”? — Major hypothesized mechanisms

Although research is not 100% conclusive, there are four major groups of hypotheses frequently discussed in the scientific literature:

5.2.1 Hyperexcitability of the temporal lobe / olfactory cortex

Most evident in temporal lobe epilepsy.

When the brain is about to seize, or in an irritative zone, cells in the piriform cortex, amygdala, and medial temporal lobe fire abnormally and intensely.

Because these regions normally handle olfactory processing, the brain interprets this abnormal firing as “smell signals.”
→ The patient suddenly experiences a strange smell, even though nothing is actually present.

Once the seizure passes or the abnormal firing stops, the smell disappears as if it never happened.

This mechanism neatly explains the pattern of “very short olfactory hallucinations lasting seconds to minutes” before seizures.

5.2.2 Imbalance in sensory–limbic–prefrontal circuits (in psychotic disorders)

In schizophrenia spectrum and other psychotic disorders:

It is believed that there are abnormalities in glutamate–GABA–dopamine systems within networks connecting:

Sensory cortex
Limbic system
Prefrontal cortex

These networks normally work together to:

Filter out noise in incoming signals
Decide how “reliable” a perception is
Distinguish between “inputs from the external world” and “signals from inside or imagination.”

When these circuits are imbalanced:

The brain may allow weak or random firing from the olfactory system to pass through unfiltered.

The prefrontal–limbic network then “tags” this as a real percept, instead of noise.

It may also link it to existing delusional content. For example:

A person with a delusion that the house will burn down → the brain “generates” a burning smell that is congruent with this belief.
A person who believes they are decomposing or dead → the brain generates a rotting corpse smell to match.

The result = olfactory hallucinations with thematic content that fits the person’s delusions, often accompanied by hallucinations in other modalities (auditory/visual).

5.2.3 Peripheral damage + central maladaptation (phantom limb–like concept)

In cases of post-viral smell disorder, post-COVID, nasal trauma, etc.:

The olfactory epithelium or nerve fibers may be damaged, so input from the nose becomes weaker, missing, or distorted.

The brain, which is used to certain patterns of olfactory input, suddenly lacks information or receives incomplete data.

The central nervous system may adapt in a maladaptive way (maladaptive plasticity):

Causing random or synchronous firing in the olfactory cortex.
Similar to phantom limb pain, where someone who has lost a limb still feels pain in the missing limb.

Result:

The person experiences phantom smells despite there being no real stimulus in the air.

Some have both phantosmia and parosmia at the same time (real smells are distorted + non-existent smells appear alternately).

5.2.4 Neurodegeneration and degeneration of the olfactory pathways

In neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease:

The olfactory system is often one of the earliest systems to degenerate.

Reduced volume in the olfactory bulb, olfactory cortex, and related pathways is frequently observed.

Patients often start with hyposmia/anosmia/parosmia.

Some also report phantosmia/olfactory hallucinations, particularly in stages where psychosis or visual hallucinations are present.

In summary:

The olfactory pathways are a “fragile point” in the brain because they connect to the limbic system and are easily affected by inflammation or degeneration. Once the circuit is disrupted or firing becomes abnormal, the brain has an increased chance of “creating smells on its own.”

6. Causes & Risk Factors — Causes and risk factors for Olfactory hallucinations

This section on the website is meant to show readers clearly that “phantom smells are a symptom that can arise from many different diseases”—there is no single answer, and it does not always mean the person has a purely psychiatric illness.

A practical framework is to classify causes based on the origin of the problem:

ENT / peripheral

Neurological

Psychiatric

Drugs / medical / systemic

Idiopathic & psychosocial factors

6.1) ENT / Peripheral causes — Problems in the nose/nasal cavity/sinuses

This group involves problems in the “front-end smell reception system” before signals enter the brain.

Main examples:

Post-viral smell dysfunction (including post-COVID-19)

After upper respiratory viral infections (e.g., influenza, SARS-CoV-2), cells in the olfactory epithelium may be damaged.

This leads to abnormal recovery → parosmia / phantosmia.

In post-COVID cases, many reports describe patients smelling burning, garbage, or smoke even when nothing is there.

Chronic rhinosinusitis / chronic allergic rhinitis

Chronic inflammation, mucus, and thickened mucosa.

Distorts olfactory input, turning it into noisy signals.

Some cases report intermittent phantosmia along with nasal congestion/sinus pain.

Nasal polyps / structural abnormalities of the nasal cavity

Obstruction + inflammation can alter receptor function.

Not everyone with nasal polyps develops phantosmia, but it is a risk factor for smell disorders.

Nasal/sinus surgery or nasal trauma

Can damage structures and nerves.

During recovery, the brain may misinterpret signals, resulting in phantosmia/parosmia.

Exposure to airborne chemicals/irritants and heavy smoking

Harsh chemicals (solvents, smoke, irritating gases) can damage the olfactory epithelium.

Chronic heavy smokers have a higher risk of olfactory dysfunction.

Overall:

ENT-related cases usually come with other symptoms such as nasal congestion, runny nose, sinus pain, and odd smells from one side of the nose.

Treatment mostly focuses on reducing inflammation, restoring olfaction, and smell training, rather than using psychiatric medications as first-line interventions.

6.2) Neurological causes — Problems in the brain and nervous system

This is a very important category, especially when phantom smells coexist with other neurological symptoms.

Main causes:

Temporal lobe epilepsy (TLE)

This is a classic cause of olfactory hallucinations.

Patients often report sudden strange smells (burning, rubber, rot) for seconds–minutes before seizures.

This serves as an “olfactory aura”—a warning sign that a seizure is imminent.

It may come with deja vu, intense fear, or brief visual phenomena.

Brain tumors (especially in frontal/temporal lobes, olfactory groove meningioma)

Tumors can compress or disrupt the function of the olfactory bulb, tract, or cortex.

This can cause a range of smell distortions: hyposmia, parosmia, and phantosmia.

Often accompanied by chronic headache, seizures, or changes in personality.

Stroke or focal lesions in the olfactory pathways

If an infarct or hemorrhage affects areas involved in smell processing,

The person may develop smell deficits plus hallucinations during recovery from the lesion.

Head trauma / Traumatic brain injury (TBI)

Blows to the brain or skull base can damage the olfactory nerve/bulb.

Maladaptive plasticity during recovery can lead to phantosmia.

Neurodegenerative diseases

Parkinson’s disease – olfactory dysfunction is often an early symptom.

Alzheimer’s disease and other dementias – olfactory pathways degenerate along with limbic structures.

Patients may exhibit hyposmia, parosmia, and phantosmia, especially in stages where psychosis emerges.

Migraine aura

There are case reports of olfactory hallucinations (e.g., smoke or burning smells) as part of a migraine aura.

The mechanism likely involves cortical spreading depression affecting olfactory cortex regions.

Neurological red flags to watch for:

Phantom smells + seizures / loss of consciousness / memory gaps

Phantom smells + severe or chronic headache

Phantom smells + focal weakness/numbness + slurred speech

→ Such cases should be referred to neurology for MRI/CT/EEG evaluation.

6.3) Psychiatric causes — When phantom smells are part of psychosis

Although most people think of “hearing voices” when they hear the word psychosis, olfactory hallucinations can also occur in psychiatric illnesses, especially in the schizophrenia spectrum and mood disorders with psychotic features.

Key disorders:

Schizophrenia and schizoaffective disorder

Some studies report that 11–80% of people with schizophrenia have experienced olfactory hallucinations at least once (wide range due to differing criteria and methods).

They typically occur along with auditory hallucinations (voices insulting/commanding) and delusions.

The theme of the phantom smell often matches the delusional content, for example:

Delusion of being decomposed/dead → smelling corpse-like odors from oneself.
Delusion of being poisoned → smelling chemicals/medicine in food.

Bipolar disorder and major depressive disorder with psychotic features

During manic or depressive episodes with psychosis, olfactory hallucinations can occur alongside auditory/visual hallucinations.

Example: depression with nihilistic delusions + olfactory hallucinations (smelling decomposing bodies).

Delusional disorder (especially somatic / persecutory / somatic–olfactory themes)

DSM notes that tactile/olfactory hallucinations may be present in delusional disorder if they are congruent with the delusional theme and not prominent enough to warrant a schizophrenia diagnosis.

For example:

A person who believes they are being gassed with poison may smell gas that is not there.
A person who believes their body is rotting may smell decay coming from themselves.

Some anxiety disorders (rare)

There are case reports of patients with anxiety who have isolated olfactory hallucinations without other psychotic features.

It is hypothesized that severe stress/anxiety may trigger abnormal firing in sensory–limbic networks.

Combined with Olfactory Reference Syndrome (ORS) / body dysmorphic spectrum

ORS centrally involves a fixed belief that “I smell bad.”

Some reports describe patients who also experience actual phantom smells (e.g., smelling their own bad odor even when alone).

The mechanism likely involves a mixture of delusional belief and sensory distortion.

Overall:

On the psychiatric side, clinicians do not view olfactory hallucinations in isolation; they assess the entire psychotic syndrome.

Risk factors include: prior history of psychosis, mood disorders, family history of psychotic illness, and substance use.

6.4) Drugs / Substances / Medical factors — Medications, chemicals, and physical illnesses

This category includes factors that “disturb the nervous system,” centrally or peripherally, and can cause smell hallucinations.

Examples:

Medications that affect olfaction or the CNS

Some drugs in the anti-epileptic, anti-depressant, and anti-psychotic classes have been reported to alter smell perception.

Certain chemotherapy agents can damage the olfactory epithelium.

Substances / intoxicants

Substances that act directly on the brain (e.g., stimulants, hallucinogens, solvent inhalation, etc.) can cause hallucinations in many modalities, including olfactory.

Radiation/chemotherapy to the head and neck

These can damage the olfactory epithelium or nerve.

They can lead to smell distortions and phantosmia.

Complications from physical illnesses

Some metabolic or endocrine conditions (e.g., liver disease, kidney failure, uncontrolled diabetes, thyrotoxicosis, etc.) can impair brain function and cause delirium.

In delirium, multiple types of hallucinations may occur, including olfactory.

6.5) Idiopathic / unknown + psychosocial risk factors

There are patients who, even after thorough investigation, have no clearly identifiable cause (idiopathic phantosmia).

Common features in this group:

High levels of stress, anxiety, and major life events (severe life stressors).

Sleep disturbance, burnout, emotional exhaustion.

Some population studies show that olfactory hallucinations are associated with higher anxiety and stress levels, even when criteria for a full psychotic disorder are not met.

Thus, for website writing, you can summarize that:

Besides clear causes (ENT, neurological, psychiatric), there is a group with “hypersensitive olfactory/brain systems + high stress + poor sleep” → leading to intermittent phantom smells even though no organic lesion can be found.

Management for this group usually focuses on psychoeducation, stress reduction, sleep hygiene, and sometimes medication/psychotherapy.

6.6) Short overall summary for general readers

The causes of olfactory hallucinations can be roughly divided into:

Problems in the nose/nasal cavity (e.g., after colds/COVID, sinusitis, nasal tumors, chemical exposure).

Problems in the brain/nervous system (temporal lobe epilepsy, brain tumors, dementia, Parkinson’s disease, head injury).

Psychiatric problems (schizophrenia, bipolar disorder, depression with psychosis, delusional disorder).

Effects of medications, substances, radiation, chemotherapy, or other physical diseases.

And some people have no clear identified cause (idiopathic) but are linked to high stress/anxiety and abnormal sleep.

7. Treatment & Management — Approaches to treatment and management

Golden principle:

“Treat the underlying cause” + help the patient cope with phantom smells in daily life.

7.1) Initial assessment

Detailed history-taking

Character of the smell, frequency, and duration of each episode.

What illness did it follow? (e.g., influenza, COVID, head trauma, sinusitis).

Are there symptoms of nasal congestion, nasal discharge, or sinus pain?

Any neurological symptoms (seizures, blackout, migraine-type headaches, focal neurological deficits)?

Any psychological symptoms (delusions, hearing voices, insomnia, depression/mania, etc.)?

Physical examination / ENT / neurological exam

Further investigations as indicated:

Nasal endoscopy / CT scan of the sinuses

MRI brain (especially to check for tumors/lesions)

EEG if temporal lobe epilepsy is suspected NCBI+2Dr.Oracle+2

7.2) Treating the underlying cause

ENT / peripheral phantosmia SmellTaste+5Cleveland Clinic+5NCBI+5

Treat sinusitis, allergic rhinitis, nasal polyps (e.g., anti-inflammatory drugs, nasal steroid sprays, saline irrigation, surgery if necessary).

Post-viral / post-COVID smell dysfunction:

Smell training (regularly practicing smelling several different odors).

Some approaches use vitamins, omega-3, or steroids under physician supervision (evidence still limited).

Neurological causes

Temporal lobe epilepsy → antiepileptic drugs, adjusted by neurologists.

Brain tumors → surgery/radiation/chemotherapy as determined by neurosurgical teams.

Stroke, neurodegeneration → treat the primary condition + rehabilitation.

Psychiatric causes Psychiatrist.com+1

If the symptom is within schizophrenia / schizoaffective disorder / bipolar disorder / MDD with psychosis:

Antipsychotic medication is the foundation.

Mood stabilizers / antidepressants as indicated by the primary diagnosis.

Psychotherapy (e.g., CBT, supportive therapy) helps patients cope with hallucinations and reduces distress.

For ORS:

Treatment resembles that for OCD/BDD more than hallucination-focused treatment: SSRIs and CBT (focusing on beliefs and misinterpretations) rather than targeting hallucinations per se.

7.3) Specific measures for phantosmia (based on systematic reviews)

Systematic reviews have found multiple options for managing phantosmia, but evidence remains limited, for example Wiley Online Library+1:

Observation (watchful waiting) – some cases improve spontaneously (especially post-viral).

Medical therapy – drugs like anticonvulsants, antipsychotics, antidepressants, local anesthetic sprays, etc., used case-by-case.

Surgical intervention – such as excision of olfactory mucosa in severe, refractory cases that do not respond to other treatments (only in highly selected cases).

7.4) Supporting quality of life

Psychoeducation — explaining to patients that “many people experience this; it isn’t just a fantasy,” so they don’t feel crazy or alone.

Suggest avoiding triggers if identifiable (certain environments or foods that provoke phantom smells).

Grounding / mindfulness techniques — focusing on other senses, checking with others whether they also smell it, to help differentiate “external vs. internal.”

Family support — ensuring that people around the patient understand that this is not “just overthinking,” but a real symptom of the nervous system.

For your website, you can emphasize:

“Having olfactory hallucinations does not automatically mean someone has a psychiatric illness, but it is a sign that they should see a doctor to investigate possible causes.”

8. Notes — Key points and important considerations

Isolated symptom but serious

An isolated olfactory hallucination can be a sign of serious brain disease (e.g., TLE, tumor), even without other visual/auditory hallucinations. PMC+2Cureus+2

Usually unpleasant odors

Burning, rotten, smoke, and chemicals often cause very high distress. Some patients can barely eat or sleep.

Must differentiate from ORS and parosmia

ORS = essentially a delusion about one’s own smell.

Parosmia = there is an odor, but it is “distorted,” e.g., coffee smells like garbage.

Phantosmia = smelling something when there is no odor source at all.

Association with anxiety and severe life events

A population study found associations between olfactory hallucinations and high anxiety and stressful life events, which can be both causes and consequences of phantosmia. ScienceDirect

Research on treatment is still limited

High-quality RCT evidence is scarce.

Most literature consists of case reports and case series → you can honestly write that “treatment approaches are still under development.”

Key message for general readers

If someone has strange smells that persist for more than 2–4 weeks, or if they occur along with other symptoms (seizures, severe headache, one-sided weakness, weight loss, psychiatric symptoms), they should see a doctor (ENT or neuro/psych depending on associated signs) and not self-diagnose.

Read Schizophrenia

References — Olfactory hallucinations / Phantosmia / ORS

It’s recommended to pick around 6–10 of these and rotate them across posts so your site looks professional and not spammy with the same sources.

Gillette B. Phantosmia. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023–2024. NCBI+1
Cleveland Clinic. Phantosmia (Olfactory Hallucinations): Causes & Treatment. Cleveland Clinic
Mayo Clinic. Phantosmia: What causes olfactory hallucinations? Mayo Clinic
Saltagi MZ, Rabbani CC, Ting JY, Higgins TS. Management of long-lasting phantosmia: a systematic review. Int Forum Allergy Rhinol. 2018;8(7):790–796. Wiley Online Library+1
MdSearchlight. Phantosmia. Patient education article on causes and classification (central vs peripheral). MD Searchlight
Cleveland Clinic. Dysosmia (Disordered Smell Perception). Cleveland Clinic
Feusner JD, Phillips KA, Stein DJ. Olfactory Reference Syndrome: Issues for DSM-V. Depress Anxiety. 2010;27(6):592–599. PMC+1
Feusner JD. Olfactory reference syndrome: problematic preoccupation with perceived body odor. International OCD Foundation. International OCD Foundation
Amin MA, et al. Short duration phantosmia changes in a post-COVID-19 patient. Case report. PMC
Wehling E, et al. (if you want to add) – population-based data on olfactory hallucinations (use in main prevalence section).

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