A red patch in the mouth: when is it harmless, and when must it be examined?

The lining of the mouth is thin tissue with a rich blood supply. When it is inflamed, thinned or irritated, it looks red. So a red patch is not the sign of one disease but the shared appearance of many different conditions. Among the causes of inflammation inside the mouth (stomatitis), MSD Manuals lists ill-fitting dentures, broken or sharp teeth, a habit of biting the cheeks and lips, acidic foods, sensitivity to ingredients in toothpaste and mouthwash, fungal and viral infections, some vitamin deficiencies and medicines.

In denture wearers, the commonest cause is denture stomatitis: reddening and inflammation of the palate tissue covered by an upper denture, linked to the layer of microbes, including the Candida fungus, that builds up on the inner surface of the denture. Cleveland Clinic writes that, depending on the study, it is seen in up to 67% of denture wearers, and that it is more common in people with full dentures than in those with partial or implant-supported dentures. There is a telling observation you can make at home here: look in the mirror and compare the edge of the redness with the edge of the denture. If the redness matches the area the denture covers exactly and does not spill beyond it, the cause is most likely the denture.

A fungal infection (candidiasis) does not always appear as white plaques; it can also show up as a red, burning area. MSD Manuals lists diabetes, HIV or a weakened immune system for another reason, and recent use of antibiotics as a history that points to thrush. With thrush that has white plaques, wiping gently with gauze lifts the plaque and leaves a red surface underneath. In smokers, and especially pipe smokers, a thickened whitish surface with red dots at the openings of the small salivary glands can be seen on the palate; MSD Manuals calls this nicotinic stomatitis.

Injuries and burns are the third large group. Hot soup or a cheesy mouthful burns the palate, a hard crisp scratches the cheek, the edge of a broken tooth rubs against the side of the tongue. What these kinds of redness have in common is that the cause is remembered and they clear quickly once the cause is removed. Red dots the size of a pinhead on the hard or soft palate show blood leaking from small vessels. Show dots that fade quickly and come with no other symptoms at your next dental appointment. But if they come with easy or unexplained bruising and bleeding, marked tiredness, paleness or fever, the NHS asks you to get an urgent GP appointment or contact 111 (England's non-emergency health line); in Turkey that means seeing your family doctor the same day; the doctor requests an urgent blood test if needed.

The picture that really needs attention is erythroplakia. The expert group convened by the WHO Collaborating Centre for Oral Cancer lists erythroplakia among the precancerous changes in the mouth (potentially malignant disorders). By definition, it is a red area that cannot be explained by another disease. Cleveland Clinic writes that these patches are slightly raised or flat red areas and may bleed when scraped. A review of erythroplakia reports that the soft palate, the floor of the mouth and the inside of the cheek are common sites, that the lesions typically stay smaller than 1.5 centimetres, that they are seen in middle and older age, and that they are strongly linked with smoking and alcohol.

Tissue examination shows why erythroplakia is taken seriously. In the data reported in the same review, invasive cancer was found in 51% of uniform, smooth red erythroplakias, cancer confined to the surface (carcinoma in situ) in 40%, and mild or moderate cell changes (dysplasia) in only 9%. In a systematic review that gathered transformation rates, the rate varied across a very wide range, from 2.6% to 65% depending on the study, with an average calculated at around 30%. These figures come from a small number of studies, and the authors of both reviews write that more studies are needed; they do not tell you your personal risk. What they do tell you is this: with a red area that has no cause, taking a tissue sample rather than waiting is the right decision.

The good news is that erythroplakia is rare. In the same systematic review, its frequency in the population was found to be between 0.04% and 1.14%, depending on the study. So in the great majority of people who see a red patch in their mouth, the cause is one of the harmless conditions listed above. The practical way to tell them apart is time: Cleveland Clinic advises seeing a doctor about new patches and sores in the mouth that have not gone within two weeks. With redness that has a clear cause, the cause is removed first and it is looked at again two weeks later; if it has not gone, or if there was never any cause, a tissue sample is discussed.

One last note concerns screening devices. Some centres may offer to screen the inside of the mouth with a special light, a dye or a saliva test. The American Dental Association (ADA) guideline writes that none of these adjunctive methods has shown enough accuracy in identifying a suspicious lesion, and that for a suspicious lesion the only important recommendation is an immediate biopsy or referral to a specialist. A red patch that comes back clear on light-based screening does not mean a biopsy is not needed.

In the pictures in the first list, the cause is clear, and improvement is expected within two weeks once it is removed. If a single item from the second list applies to you, stop watching it.

For a red patch, your first port of call is your dentist. When a biopsy is needed, oral and maxillofacial surgery, oral medicine or ear, nose and throat comes in.

1. 1

   History: when did you notice it, and is there a cause

   You are asked about dentures, burns, a new toothpaste or mouthwash, antibiotics, smoking and alcohol. If you have taken photos since the day you first noticed the patch, show them; this is how the clinician sees whether it has grown.

2. 2

   The whole mouth and the neck are examined

   The ADA recommends a visual and hands-on examination of the inside and outside of the mouth in all adults. The site, colour, borders, surface and firmness of the patch and the lymph nodes in the neck are assessed.

3. 3

   Any cause is removed

   The denture is adjusted or you are asked to take it out at night, a sharp edge is smoothed, thrush is treated, and a suspect toothpaste or mouthwash is stopped.

4. 4

   Follow-up appointment

   For lesions that do not look suspicious, the ADA recommends seeing the patient again at regular intervals, and a biopsy or referral to a specialist if the lesion has not gone and a precancerous change cannot be ruled out. Get the follow-up date before you leave the appointment.

5. 5

   If there is any doubt, a tissue sample straight away

   For a lesion with no cause, or one that looks suspicious, the ADA recommends a biopsy without waiting or immediate referral to a specialist. A small piece is taken under local anaesthetic and sent to pathology.

6. 6

   A plan based on the result

   If a harmless condition is found, watching; if cell changes (dysplasia) are found, removal of the lesion and close follow-up; if cancer is found, referral to the head and neck team.

There is no single treatment for a red patch; first the cause is made clear.

The following are the decisions that most often waste time. We set them out so that, whichever clinician you see, you can ask the right questions.

The times below are the expected framework for redness with a clear cause. The plan of the clinician who examines you takes priority.

1. The first days

   Burns and scratches heal noticeably within a few days. During this time, stay away from acidic and hot food.

2. The two weeks after the cause is removed

   If the denture has been adjusted, the sharp edge smoothed or the thrush treated, the redness is expected to recede within this time. Cleveland Clinic advises seeing a doctor about patches that have not gone in two weeks.

3. After two weeks

   For a red area that has not gone, a biopsy or referral to a specialist should be discussed. The ADA recommends a biopsy if the lesion has not gone and a precancerous change cannot be ruled out.

4. After biopsy and treatment

   If cell changes or erythroplakia are diagnosed, follow-up appointments continue for a long time.

We do not give a single figure here, because behind a red patch in the mouth there may be inflammation that clears with denture cleaning, or a lesion that calls for a biopsy and surgery. These are the items that determine the scope:

The cause

Denture stomatitis, thrush, injury and erythroplakia take entirely different routes.

Biopsy and pathology

Taking the tissue sample and examining it in pathology are separate items.

Denture or tooth adjustment

Adjusting or replacing a denture, or repairing a sharp tooth edge, are separate items of dental treatment.

Length of treatment and follow-up

With lesions that have been removed, follow-up appointments continue for a long time.