Anosmia in COVID infection

It happens because the virus can affect the olfactory system, which is responsible for detecting smells. The exact mechanism isn’t fully understood, but it's believed that the virus targets cells in the nasal passages that cause congestion, specifically the supporting cells that help neurons function. These neurons, which send smell signals to the brain, aren’t typically infected by the virus itself, but they rely on these supporting cells to stay active.

As a result, the ability to smell can be temporarily blocked or diminished. This often occurs without the usual signs of a stuffy nose, so you may not even have other cold-like symptoms. Anosmia can happen suddenly and may be one of the first signs of infection, even before other symptoms like fever or cough appear.

While the loss of smell due to COVID-19 can be alarming, it’s generally temporary. Many people report regaining their sense of smell within a few weeks. However, for some, recovery can take longer, and in rare cases, it may not fully return. If anosmia persists after recovery, it’s worth consulting a healthcare provider for further evaluation.

COVID-19 affects everybody differently, it is therefore difficult to predict how long anosmia may affect you. As a general rule it appears that 9 out of 10 people with COVID-related anosmia can expect a substantial improvement in their sense of smell within 4 weeks of their infection. Others can take several months or even longer to return and for a small number their sense of smell may not return – however, recent studies suggest that persistent COVID-19 related anosmia has an excellent prognosis with nearly complete recovery at 1 year for most people.

Many find they experience distorted smells as the sense returns, or imagine smells that aren’t there, a phenomenon known as phantosmia or olfactory hallucination, which can be distressing if they are unpleasant smells, but it’s a sign of the nerves regenerating and usually settles over time.

The majority of people will gradually regain their smell. Research shows that 90% of people fully recover, but it can take up to 18 months to regenerate olfactory cells, depending on where in the olfactory system the virus has damaged, and for some, it will unfortunately be permanent damage.

Research is ongoing as to whether surgical techniques may prove effective. In the meantime, the mainstay of treatment is smell retraining therapy, a short course of steroid tablets (although these should not be used during the initial COVID-19 infection), or a steroid nasal spray that your doctor can prescribe. The retraining therapy has had reasonable results, but there is mixed success with the other methods.

Smell retraining therapy works by slowly reintroducing yourself to distinct smells, in the hope that it can stimulate the olfactory system in the brain to remember how to smell. The four categories that are advised to retrain are floral, such as rose, fruity, like orange, spicy, like cloves, and a category called resinous, which eucalyptus fits into.

The retraining technique involves taking gentle sniffs of each scent in order, for 20 seconds at a time, twice a day, and concentrating on the memory of that smell. This should be done for at least 3 months.

Support is available from charities such as Fifth Sense & AbScent.

There are safety implications, if you can't smell burning or gas leaks, so make sure you have smoke alarms at home and work, and test them regularly. If you have gas hobs, buy some gas sensors in case there's a leak. Ensure household members and co-workers are aware that you will not be able to smell any danger, so they can be more vigilant.