Loss of Smell: Causes, Investigation, and Treatment Options
- 3 days ago
- 5 min read
Written by Mr Tim Biggs | Consultant ENT Surgeon | Rhinology & Facial Plastics
Why Loss of Smell Matters
The sense of smell is deeply connected to quality of life in ways that are often underappreciated until it is lost. Smell informs our experience of food and drink, alerts us to danger such as gas leaks, smoke, and spoiled food, and is intimately linked to memory and emotional experience. Its loss or distortion can cause significant distress, nutritional consequences from reduced appetite, and a sense of disconnection from daily pleasures that affects mental health.
Despite this, anosmia and hyposmia are frequently dismissed in primary care, with patients often told that nothing can be done. In many cases, that is not true. A thorough specialist assessment can identify the cause, guide treatment, and in many patients produce meaningful improvement.
Understanding the Terminology
It is helpful to be precise about terms:
• Anosmia: complete absence of the sense of smell
• Hyposmia: reduced sense of smell, present but impaired
• Parosmia: distorted smell, where odours are perceived differently from normal, often as unpleasant or foul, even when the stimulus is normally pleasant
• Phantosmia: perception of smell in the absence of any olfactory stimulus
Parosmia and phantosmia are particularly common during recovery from post-viral olfactory loss and, while distressing, are generally positive prognostic signs indicating that olfactory nerve fibres are regenerating.
The Main Causes of Olfactory Loss
Conductive Anosmia: Obstruction to Airflow
For smell to occur, odour molecules must reach the olfactory cleft, the narrow area at the top of the nasal cavity where the olfactory receptor neurons are concentrated. Any condition that blocks airflow to this region can cause olfactory loss even when the olfactory nerves themselves are intact.
Nasal polyps are the most common structural cause. They can reduce or abolish smell through a combination of mechanical obstruction and direct inflammatory damage to the olfactory epithelium. Treating the polyps, whether medically or surgically, can restore smell significantly, particularly if treatment is initiated before long-standing inflammatory damage has occurred.
Significant septal deviation, severe turbinate hypertrophy, and mucosal swelling from chronic sinusitis can all reduce olfactory airflow to a degree that impairs smell. Addressing these anatomical and inflammatory factors is an important part of managing olfactory loss.
Post-Viral Anosmia
Viral upper respiratory infections have long been recognised as a cause of olfactory loss. The COVID-19 pandemic brought this into sharp public awareness, with a substantial proportion of those infected experiencing sudden anosmia, often with little or no nasal congestion, reflecting direct viral damage to the olfactory epithelium rather than simple obstruction.
Post-viral olfactory loss, whether following COVID-19 or other viruses, results from damage to the olfactory receptor neurons or their supporting cells. Recovery is variable. Many patients recover fully over weeks to months. A significant minority experience prolonged anosmia or persistent parosmia lasting a year or more. Spontaneous recovery can continue for two to three years from onset, and there is evidence that olfactory training may accelerate and enhance the recovery process.
Post-Traumatic Anosmia
Head trauma, particularly occipital or frontal impacts, can shear the delicate olfactory nerve filaments as they pass through the cribriform plate, causing sudden and often severe olfactory loss. Post-traumatic anosmia has one of the poorer prognoses for recovery, though partial improvement is seen in some patients, particularly when the loss is not complete at onset.
Sinonasal Inflammatory Disease
Chronic rhinosinusitis, with or without nasal polyps, causes olfactory loss through a combination of obstructed airflow and inflammatory damage. The eosinophilic mucosal inflammation characteristic of polyp disease is particularly damaging to the olfactory epithelium. Aggressive treatment of the underlying inflammatory disease is the priority.
Idiopathic Anosmia
In a proportion of patients, no identifiable cause is found despite thorough investigation. This may represent unrecognised viral damage, early neurodegenerative change, or ageing-related olfactory decline. MRI of the brain and olfactory tracts is considered in selected cases to exclude intracranial pathology.
Investigation at Consultation
A thorough assessment for olfactory loss includes a detailed history, nasal endoscopy, and olfactory testing using validated psychophysical tools such as Sniffin' Sticks, which quantify smell threshold, discrimination, and identification. This provides a reproducible baseline and allows monitoring of treatment response over time.
CT scanning of the sinuses identifies structural disease and polyps. MRI is arranged where central pathology is a concern or where the clinical picture is atypical. Blood tests may identify systemic causes such as zinc deficiency, hypothyroidism, or autoimmune disease.
Treatment Options
Treating the Underlying Cause
Where olfactory loss is caused by a treatable condition, addressing that condition is the priority. In nasal polyp disease, a combination of high-dose nasal steroid drops, oral steroid courses, and where appropriate FESS can produce significant improvement in smell. In chronic sinusitis, restoring sinus ventilation may allow the olfactory epithelium to recover. Biologic therapy with dupilumab has shown particular promise in recovering smell in eosinophilic polyp disease.
Olfactory training is a structured rehabilitation technique with good evidence in post-viral anosmia. It involves smelling a set of four strong odorants, traditionally rose, eucalyptus, lemon, and cloves, for 20 seconds each, twice daily, over a minimum of three months. The mechanism appears to involve stimulation of olfactory neurogenesis and central olfactory cortex plasticity. I recommend it routinely to patients with post-viral olfactory loss alongside any other treatments. Click here to find out more.
Pharmacological Approaches
Systemic and topical corticosteroids benefit anosmia driven by sinonasal inflammation. Omega-3 fatty acid supplementation and alpha-lipoic acid have been studied with modest positive data. There is emerging interest in intranasal platelet-rich plasma (PRP) injections, though this remains investigational. I discuss these options honestly, with reference to the available evidence, at consultation.
Arrange a Consultation
If you have experienced loss of smell, whether recently or over a prolonged period, a specialist assessment is worthwhile. Identifying the cause, quantifying the degree of loss, and initiating appropriate treatment early gives the best chance of recovery.
I see patients privately. To arrange a consultation, please contact my secretary Michele Hewlett. Fees are available at www.hampshireentclinics.co.uk.
Frequently Asked Questions
What is anosmia?
Anosmia is the complete loss of the sense of smell. Hyposmia refers to a reduced sense of smell. Parosmia describes distorted smell perception, which is common during recovery from post-viral olfactory loss.
Can you lose your sense of smell permanently?
This depends on the cause. Conductive anosmia from obstruction often improves with treatment. Post-viral anosmia frequently improves over months to years. Post-traumatic and idiopathic anosmia carry more variable prognoses.
What is olfactory training and does it work?
Olfactory training involves deliberately smelling a set of strong scents twice daily over several months. Evidence supports its use in post-viral anosmia, where it appears to stimulate olfactory nerve regeneration and central adaptation.
Can nasal polyps cause complete loss of smell?
Yes. Nasal polyps cause anosmia both by obstructing airflow to the olfactory cleft and by producing inflammatory mediators that directly damage the olfactory epithelium. Early treatment offers the best chance of smell recovery.
Is parosmia a sign of recovery?
In most cases, yes. Parosmia following post-viral olfactory loss is often a sign that olfactory nerve fibres are regenerating. Most patients with parosmia experience continued improvement in smell quality over time.
Where does Mr Tim Biggs assess and treat loss of smell?
Mr Biggs assesses privately in Hampshire.
How do I arrange a consultation for loss of smell?
Contact Michele Hewlett, Mr Biggs's secretary. Fees are available at www.hampshireentclinics.co.uk.
