Smell disorders

Summary

Smell disorders range from a reduced sense of smell to complete loss or distorted odours. They may be quantitative—reduced smell (hyposmia) or loss of smell (anosmia)—or qualitative, such as distorted smells (parosmia) or perceiving an odour that is not present (phantosmia). Causes include nasal inflammation or blockage, viral infection, surgery, head injury, medication, ageing and neurological or systemic disease.

Some causes can be treated. Nasal corticosteroids or surgery may help when inflammation, polyps or another physical blockage prevents odours from reaching the smell area. When the smell epithelium or nervous system has been injured, recovery is less predictable, but improvement can occur and structured smell training may help. Practical safety measures remain important while smell is reduced.

How smell works

Smell contributes greatly to flavour and also warns us about smoke, gas and spoiled food. Odour molecules reach specialised receptors high in the nose. Signals travel through the olfactory nerves to brain regions involved in recognising odours, memory and emotion.

Causes and assessment

Common causes include a cold or other viral infection, chronic rhinosinusitis, nasal polyps, allergy, head injury and ageing. Less commonly, medicines, exposure to harmful chemicals, surgery, endocrine or neurological conditions and tumours can contribute. A sudden smell loss can occur with viral infections even without marked nasal blockage.

Assessment includes the timing and pattern of the change, associated nasal or neurological symptoms, medication and relevant exposures. The ENT specialist examines the nose and may use nasal endoscopy. A validated smell-identification test can measure function. Imaging or other tests are reserved for selected cases.

Treatment and recovery

Treatment is directed at the cause. Inflammatory nasal disease may respond to saline rinsing and a prescribed corticosteroid spray; polyps or structural blockage sometimes require additional treatment or surgery. Do not use systemic corticosteroids or stop medication without medical advice.

Smell training involves sniffing a set of distinct odours regularly for several months and is commonly recommended for post-viral, post-traumatic and unexplained smell loss. Recovery varies: some people improve spontaneously, particularly after viral illness, while others have persistent loss. Distorted smells can occur during recovery.

Living safely with reduced smell

• Install and regularly test smoke alarms. Use a carbon-monoxide detector where relevant.
• If your home uses gas, consider a gas detector and ask others to check if you suspect a leak; never rely on smell alone.
• Check expiry dates, storage temperatures and the appearance of food. Ask another person when unsure whether food is spoiled.
• Maintain good nutrition by varying texture, colour, temperature, herbs and spices without adding excessive salt or sugar.
• Seek medical advice for unexplained weight loss, poor intake or a persistent new smell disorder.

Seek urgent medical assessment when smell loss follows significant head injury or occurs with weakness, facial droop, severe headache, confusion, visual symptoms or other sudden neurological signs.