Since we launched last year, the ZOE COVID Symptom Study app has helped to identify or confirm many important symptoms of COVID-19, including loss of smell (anosmia), skin rashes and sudden confusion (delirium).

Now another potential new symptom has emerged: ‘COVID tongue’ - changes to the mouth or tongue caused by COVID-19.‍

What do we know about COVID tongue?‍

As well as asking questions about a fixed set of different symptoms that might be COVID-19, such as fever, headaches or fatigue, the ZOE COVID Symptom Study app also asks contributors to write in any unusual symptoms they are experiencing.

For a while we’ve been noticing an increasing number of people reporting that their tongue doesn’t look normal, particularly that it is white and patchy. 

Professor Tim Spector, COVID Symptom Study lead, tweeted about this in January and got a lot of responses - and some pictures! - from people saying they had noticed changes to their mouth or tongue when they had COVID-19. 

Our observations are supported by a review of studies reporting changes to the mouth or tongue in people with COVID-19, published in December. 

The researchers found that having a dry mouth was the most common problem, followed by loss of taste (dysgeusia) and fungal infection (oral thrush). 

They also reported changes in tongue sensation, muscle pain while chewing, swelling in the mouth and ulcers on the tongue or inner surface of the mouth and lips. ‍

What causes COVID tongue?‍

Right now we don’t know what causes COVID tongue or other changes to the mouth such as ulcers or swelling. 

It might be a direct effect of viral infection, or it could be a more general immune related response to being ill. 

Another possibility is that people with COVID-19 may be more susceptible to fungal infections in their mouth (oral thrush), which show up as white blotches, although sufferers often report having been unsuccessfully treated with anti-fungal drugs.‍

How common is COVID tongue?‍

In September last year, researchers in Spain published a paper reporting that around a quarter of patients hospitalised with COVID-19 had changes to their mouth or tongue. 

We don’t think COVID tongue is as common in mild Covid-19 disease, but we don’t yet know how common it is in the wider community or how reliable it is as a symptom of COVID-19. 

Mouth ulcers are very common, and many illnesses and infections can cause changes to the surface of the tongue, such as an unexplained condition known as ‘geographic tongue’ that can last for months.

We also don’t know whether changes to the mouth or tongue can be the only symptom of COVID-19, or whether they tend to come earlier or later in the illness. 

To find out more, we’re now asking about any new mouth ulcers or changes to the tongue as part of the symptom questions in the ZOE COVID Symptom Study app.‍

If you’ve noticed any strange changes to your tongue, or unusual ulcers, especially if you’re having any other symptoms that could be COVID-19, you should download the app, log a health report and get a test. You should also self-isolate until you’re sure you’re not infected. 

Stay safe and keep logging.