Phantosmia

Phantosmia is the smelling of an odour that isn’t there. It is also called ‘olfactory hallucination’.

Hyposmia/anosmia means reduced/loss of sense of smell.

Parosmia is when people have an altered sense of smell for something that other people can smell.

Key Features

• Phantosmia is nearly always benign
• Smells are typically of something burnt, smoky, or foul but can be pleasant.
• It can follow on from loss of smell and taste – e.g., after covid-19

Phantosmia is a surprisingly common reason for referral to our neurology outpatient service. This was the case even before Covid-19 and we anticipate that there will be an increase in the problem which is why we made this factsheet.

Most people with phantosmia report it as an intermittent smell of something burnt, foul or unpleasant. Cigarette smoke and petrol are common but olfactory experiences can be varied. Sometimes it can be persistent.

What causes Phantosmia?

There are many potential causes of phantosmia although most are ‘idiopathic’. In a population study of 2569 Swedish adults over the age of 60, 5% had this symptom. Smoky/Burnt – was the runaway “smell” in this study.

Idiopathic – by far the commonest cause

Structural – much rarer. Just as people can develop Charles Bonnet visual hallucinations when they can’t see, or musical hallucinations when they can’t hear, so olfactory hallucinations can occur whenever the usual olfactory pathways, either in the nose or brain, are disrupted.

Should I be worried about neurological disease?

The answer is ‘hardly ever’, especially if 1 in 20 people already have it.

• Migraine– there is a statistical relationship with migraine, this included migraine olfactory aura but also relates togeneralised brain hypersensitivity seen in people with migraine.
• Head injury– head injury like any process associated with loss of sense of smell can trigger phantosmia.
• Focal temporal lobe seizures – Olfactory hallucination is uncommon in temporal lobe epilepsy, affecting only 5% of people with the condition. Crucially, olfactory hallucination almost never occurs as an isolated symptom in seizures.
• Other– there are case reports associating phantosmia with virtually every brain disease. But they are all rare.