What causes smelling smoke when there is no external source and how is it treated?

Smelling Smoke Without an External Source

Smelling smoke when no smoke is present is called phantosmia, a qualitative olfactory disorder where distorted smells occur in the absence of actual olfactory stimuli, and requires evaluation to identify the underlying cause—which ranges from post-viral olfactory dysfunction to neurological conditions—with treatment focused on addressing the etiology and providing symptomatic relief. 1

Understanding the Condition

Phantosmia differs fundamentally from parosmia (distortion of actual smells) because it occurs without any external olfactory stimulus. 1 This phantom smell perception can manifest as various odors, with smoke being one of the most commonly reported.

Key Etiologies to Consider

The underlying causes of phantosmia include:

• Post-viral olfactory dysfunction: Viral infections, including COVID-19, can damage olfactory neurons and cause persistent phantom odors 1
• Sinonasal diseases: Chronic rhinosinusitis and other nasal pathology may trigger abnormal olfactory signals 1
• Traumatic brain injury: Head trauma can disrupt olfactory pathways 1
• Neurological conditions: Seizure disorders, migraines, and neurodegenerative diseases (Parkinson's disease, Alzheimer's disease) can present with phantosmia 2, 1
• Psychiatric disorders: Schizophrenia and other psychiatric conditions may include olfactory hallucinations 1
• Toxic chemical exposure: Occupational or environmental exposures to irritants can damage olfactory epithelium 2
• Medications: Certain drugs may cause olfactory disturbances 1

Diagnostic Approach

The evaluation must systematically rule out serious neurological causes while identifying treatable sinonasal pathology. 1

Essential History Elements

• Onset and duration: Sudden onset suggests viral or traumatic etiology; gradual onset may indicate neurodegenerative disease 1
• Exposure history: Document any head trauma, recent viral infections (especially upper respiratory infections), toxic chemical exposures, or enclosed-space fire exposure 2, 3
• Associated symptoms: Headaches, seizures, cognitive changes, or other neurological symptoms warrant urgent evaluation 1
• Medication review: Identify potentially causative drugs 1
• Occupational exposures: Workers exposed to coal, welding fumes, organic dusts, engine exhausts, or fire smoke are at increased risk 2

Physical Examination

• Nasal endoscopy: Essential to identify sinonasal disease, polyps, or masses 2
• Neurological examination: Assess for focal deficits suggesting central nervous system pathology 1

Objective Testing

• Smell identification tests: Quantify olfactory function and distinguish phantosmia from other olfactory disorders 2, 1
• Neuroimaging (MRI/CT): Indicated when neurological symptoms are present or when phantosmia persists without clear sinonasal cause 1
• PET/CT or fMRI: May reveal brain structure changes in complex cases 1

Treatment Strategy

Unlike parosmia, phantosmia treatment is less straightforward and must prioritize identifying and treating the underlying cause rather than the symptom itself. 1

Primary Management

• Treat underlying sinonasal disease: When chronic rhinosinusitis or other nasal pathology is identified, appropriate medical or surgical management may resolve phantosmia 2, 1
• Address neurological conditions: Refer to neurology for management of seizure disorders, migraines, or neurodegenerative diseases 1
• Remove toxic exposures: Eliminate occupational or environmental irritants; implement smoke-free policies 2
• Medication adjustment: Discontinue or substitute potentially causative drugs 1

Symptomatic Relief

When the underlying cause cannot be corrected or while awaiting resolution:

• Modified olfactory training (MOT): While primarily studied for parosmia, this approach involves systematic exposure to specific odors and may provide benefit 1
• Supportive care: Focus on helping patients cope with the symptom, as recovery duration varies significantly 1
• Psychiatric support: Essential when phantosmia affects mental well-being or quality of life 1

Important Clinical Caveats

Do not confuse actual environmental tobacco smoke exposure with phantosmia. Thirdhand smoke persists on surfaces and continues to off-gas, creating real odors that may be mistaken for phantom smells. 4 If others can also smell smoke, or if the patient has been in environments where smoking occurred, this represents actual exposure rather than phantosmia. 4

In fire victims, actual smoke smell may indicate cyanide poisoning rather than phantosmia. Enclosed-space fire exposure with altered consciousness, cardiovascular changes, or elevated lactate requires immediate treatment for cyanide toxicity. 3, 5

Occupational exposures causing chronic bronchitis produce real respiratory symptoms and cough, not phantom smells. Workers exposed to fire smoke, welding fumes, or organic dusts develop actual inflammatory responses. 2

The prognosis for phantosmia varies widely depending on etiology—post-viral cases may resolve spontaneously over months, while those associated with neurodegenerative disease may persist or worsen. 1