An epidemiologist at King's College, London has claimed that there is an increase in the number of Covid patients suffering from uncomfortable mouth symptoms like oral ulcers - not yet listed by the World Health Organization (WHO) as one of the COVID-19 symptoms.

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Professor Tim Spector said in a tweet that he has seen an increase in such patients. "One in five people with Covid still present with less common symptoms that don't get on the official PHE (Public Health England) list - such as skin rashes," Spector tweeted. "Seeing increasing numbers of COVID tongues and strange mouth ulcers. If you have a strange symptom or even just headache and fatigue stay at home!" he added.

There is no mention of oral symptoms listed either by the US Centers for Disease Control and Prevention (CDC) or the WHO. Spector is leading the 'ZOE COVID Symptom Study' app which allows people to sign up and self-report any of their COVID-19 symptoms. This is not the first time Covid-19 has been linked to mouth and tongue symptoms.

Last year, research in the Nature journal Evidence-Based Dentistry detailed three COVID-19 patients who experienced oral ulceration or blistering of the mouth. Another study in JAMA Dermatology looked at 21 COVID patients in Spain who had skin rashes and found six individuals (29 per cent) also presented with an oral rash. A recent New York Times article said that COVID survivors described oral problems they're experiencing such as "teeth falling out, sensitive gums, teeth turning grey, and teeth cracking."

Studies suggest that the mouth might be a vulnerable area to coronavirus due to the abundance of the ACE2 (angiotensin converting enzyme) receptor in oral tissue. According to the WHO, the most common symptoms of COVID-19 are fever, dry cough, and tiredness. Other symptoms include loss of taste or smell, aches and pains, headache, sore throat, nasal congestion, red eyes, diarrhoea, or a skin rash.