CONCERNS over 'Covid tongue' have sparked calls for it to be recognised as an official symptom.

Epidemiologist Professor Tim Spector has said he has seen a concerning rise in the number of Covid patients showing the symptom.

'Covid tongue' is a potential symptom which gives patients sores on their tongue as well as mouth ulcers and tongue swelling.

The professor from King's College London is said to be monitoring the pandemic through his Covid symptom tracker app.

The app is used by millions of residents and has shown one in five Covid sufferers are showing symptoms not recognised by the NHS.

As a result, the professor says up to 20 percent of infectious residents may be spreading the virus without knowing they have Covid.

Currently there are only three officially recognised symptoms of Covid-19.

These are a continuous cough, a fever and a sudden loss of smell and taste.

Professor Spector said in a tweet: "One in five people with Covid still present with less common symptoms that don’t get on the official PHE list - such as skin rashes.

"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.

"Keep those Covid tongue pics coming - important to draw attention to these, skin rashes, Covid toes and the 20 plus other symptoms of Covid that go ignored.

"Thirty-five per cent of people have non-classic symptoms in the first three days when most infective."

The professor has repeatedly called on the NHS to add new symptom to their current list.

Speaking to the MailOnline, the professor added: "We're still missing 35 per cent of cases that have symptoms that aren't in the NHS 111 list which is the briefest list in the world."

"We are collecting many anecdotal reports of Covid tongue via the ZOE app and it is associated with Long Covid patients.

"We need more analyses before we can put some numbers on how common it is and how predictive it is of Covid.

"Until then, unusual tongue symptoms are likely to suggest Covid while the virus is still common."

Seven out of ten patients suffer from at least one of the officially recognised symptoms, according to NHS hospital records.

Read more: The Covid 19 symptoms to look out for in children as mum warns of potential new symptom

However, it shows up to a third of patients can experience breathing problems, stomach pains, fatigue and muscle and join pains.

Although the 'Covid tongue' could be a sign of the virus, experts also warn red and white patches can also be caused by other infections and diseases.

According to Professor Spector and fellow King's College London researcher's app, 19 symptoms have been recorded.

Millions of residents have signed up to the app to log their symptoms, creating a database.

The full list of symptoms, in order of how predictive they are of the disease, include:

1. Loss of smell/taste

2. Persistent cough

3. Fatigue

4. Loss of appetite

5. Skin rash

6. Hives

7. Fever

8. Severe muscle pain

9. Shortness of breath

10. Diarrhoea

11. Delirium

12. Abdominal pain

13. Chest pain

14. Hoarse voice

15. Eye soreness

16. Sore or painful throat

17. Nausea or vomiting

18. Headache

19. Dizziness or light headedness