What happens when you lose your sense of smell?

When you lose your sense of smell, you lose the ability to detect one or more smells. The medical word is anosmia, or smell blindness, and it may be temporary or permanent. A decreased sensitivity to some or all smells is called hyposmia. Anosmia can be acquired later in life, from causes such as upper respiratory infections, head trauma or neurodegenerative diseases, or it can be congenital, present from birth, typically because of genetic factors or developmental abnormalities.

It is more than a missing pleasure. Loss of smell can be dangerous because it hinders the detection of gas leaks, fire, chemical spills, noxious fumes and spoiled food. People who suddenly lose it may find food less appetizing, although people born without a sense of smell rarely complain of this. Congenital anosmia can even go unnoticed: because the person has never smelled anything, they may have little or no understanding of what is missing.

Many people discovered anosmia during the COVID-19 pandemic. Viruses can infect the olfactory epithelium, the smell-sensing lining of the nose, and cause a loss of smell. Estimates vary: one source says about 50% of patients with SARS-CoV-2 experience some disorder of smell, another says as many as 80% show some change in the chemical senses, including smell. In a survey of 2 million participants in the UK and US, loss of smell was more predictive of COVID-19 than fever, cough or fatigue.

The good news is that smell can sometimes come back. In smell training, people sniff strong scents regularly, each for at least 20 seconds, at least twice a day, for three to six months or more. A 2021 meta-analysis found clinically significant improvements, though critics say the studies are small and the nerves might have recovered anyway.