What causes loss of smell?

A common cold, allergic rhinitis, or chronic sinusitis can swell the lining of the nose and prevent scent molecules from reaching smell receptors. A blocked or runny nose, sneezing, facial pressure, or thick mucus can provide a useful clue. COVID-19 can affect smell even when nasal blockage is not prominent, and altered smell may continue after the infection as part of Long COVID.

Smell may also change after nasal injury, exposure to irritating substances, or less commonly a problem affecting nerves or the brain. Food may seem tasteless because much of flavour comes from smell, while salty, sweet, sour, and bitter sensations can remain.

Treat a blocked nose gently, drink fluids, and avoid smoke and strong chemical fumes. Do not insert objects into the nose. Take care with food safety because you may not detect spoilage, and check smoke and gas alarms. Note whether the change began with a cold, allergy symptoms, COVID-19, injury, or a new medicine. Arrange a review if smell does not return, keeps changing, or affects eating and safety.

Seek urgent help after a head injury if loss of smell occurs with confusion, weakness, severe headache, repeated vomiting, or a seizure. Arrange prompt medical advice for one-sided nasal blockage with bleeding, severe facial swelling, high fever, or worsening pain. Persistent or unexplained loss of smell deserves assessment, particularly when it occurs with other neurological symptoms.

Ask whether nasal inflammation, infection, a medicine, or nerve involvement is most likely; whether an examination or referral is needed; how to protect food and gas safety; and when improvement should be reviewed.