A white patch in the mouth that won't wipe off: thrush or leukoplakia?

The lining of the inside of the mouth is normally thin and pink. If an area is irritated for a long time, the cells there protect themselves by producing a thicker layer of the tough protein that covers the skin (keratin). On a wet surface, this thick layer looks white. MSD Manuals writes that leukoplakia is a flat white patch that develops in this way, through long-term irritation of the lining of the mouth. Because the layer is the tissue itself, it does not come off with scraping or brushing; this is the basic difference from a thrush coating.

Oral thrush, on the other hand, is a layer of yeast that builds up on the lining. The NHS writes that in adults with oral thrush the inside of the mouth is red with white patches on it, and that when these patches are wiped off they leave red spots that may bleed. Cracks at the corners of the mouth, a loss of taste, a bad taste in the mouth and pain in the tongue or gums can go with it. Taking antibiotics for a long time, asthma inhalers, chemotherapy, sleeping in a denture and a poorly fitting denture are among the things that make thrush more likely.

The first check you can do at home is based on this difference. Wash your hands, wrap a piece of clean gauze or a soft toothbrush around your finger, and gently wipe the white area once or twice. If the whiteness comes off and leaves a reddened surface that bleeds slightly, the picture fits thrush. If nothing changes, the patch is within the tissue; in that case the other possibilities below come to the fore. Do not press hard or scrape; the aim is to see whether the layer shifts, not to injure the lining.

The second home check is for widespread, milky whiteness on the inside of the cheek. This condition, called leukoedema (a harmless, widespread white appearance inside the cheek), is common and usually affects both cheeks at once. In a case report published in the Journal of Dental Sciences, the authors write that the whiteness disappears when the lining of the cheek is stretched, and that this stretch test is very helpful in the diagnosis. In front of a mirror, pull your cheek outwards with two fingers: if the whiteness disappears, it is most likely leukoedema. The same paper also notes that leukoedema is more common and more pronounced in smokers.

A large proportion of white patches that do not wipe off have an obvious cause. A sharp, broken tooth edge, repeatedly biting the tongue or cheek, an old filling with a sharp edge or a poorly fitting denture rubs against the same spot over and over and causes thickening. The NHS writes that the dentist first rules out causes such as a fungal infection and cheek biting. Cleveland Clinic also notes that in denture wearers the clinician checks whether the denture is rubbing against the gum or the cheek. Once the cause is removed, patches like these are expected to fade.

A study from the Netherlands shows how much this distinction matters in practice. Of 275 consecutive patients seen at a hospital in the Netherlands between 1997 and 2012 with a provisional diagnosis of leukoplakia, a definite diagnosis of leukoplakia was made in only 176, using strict clinical and pathological criteria. In some of the other patients the patch faded once a cause such as friction or a filling was removed, some did not come back for review or biopsy, and in some the diagnosis could not be confirmed by biopsy; and in 5 of the 181 patches clinically called leukoplakia, the biopsy gave a different diagnosis, two of which were cancer. The authors recommend that when an obvious cause is found, it should be removed and a wait of no more than 4 weeks allowed. The authors propose defining leukoplakia as the white patch that remains once all other white conditions that can be identified clinically and under the microscope have been ruled out.

The appearance of leukoplakia also affects its risk. Cleveland Clinic distinguishes two types: homogeneous leukoplakia, a flat white patch whose surface can be smooth, wrinkled or ridged, usually stays benign; the non-homogeneous type, which is irregular in shape, mixes white and red and can be raised, turns into cancer about seven times more often in studies. MSD Manuals writes that red, flat, thinned areas (erythroplakia) are much more worrying than a white patch. If you see red areas within the patch, the waiting time gets shorter.

What do the figures say? In a meta-analysis pooling 92 studies, published in Head & Neck, the rate at which leukoplakia turned into cancer over the follow-up period was 9.5%, with a wide confidence interval of 5.9 to 14%. The authors estimate the annual rate at about 1.56%. In the same study, the rate was 33.1% for red patches (erythroplakia), with a very wide range of 13.6 to 56.1%; 49.5% (26.7 to 72.4%) for a subtype that spreads quickly and mostly affects the gums (proliferative verrucous leukoplakia); and 1.4% for lichen planus. These rates do not mean that every patch will become cancer; most patches stay benign. But because there is no way of telling by eye which ones will stay benign, follow-up is needed.

Lichen planus deserves a separate mention. Cleveland Clinic writes that oral lichen planus appears as white lines in a web or lace-like pattern on the inside of the cheeks, white patches on the tongue or gums and sometimes bright red gums and sores, and that it is 3 to 4 times more common in women than in men. It is not considered dangerous, but because it carries a small risk of turning into cancer, it too needs regular review. A lacy pattern, a symmetrical position on both cheeks and burning with spicy or acidic food suggest this condition; the definite diagnosis is again usually made by biopsy.

The situations in the first list are usually harmless or clear with simple treatment. If a point from the second list applies, see your dentist without waiting for the 2 weeks.

The sequence below sets out the steps to expect when you go to your dentist with a white patch that does not wipe off. If a step is skipped, you can ask why.

1. 1

   History: how long it has been there, what you use

   The clinician asks how long the patch has been there, whether you smoke, use tobacco or drink alcohol, what medicines you take, whether you wear a denture and whether you have a condition that affects your immune system. If you do not know when you first noticed the patch, say so; MSD writes that patches of unknown duration should also be sent for biopsy.

2. 2

   The wipe test and cheek stretch

   Whether the patch wipes off, whether it disappears when stretched, whether its surface is smooth or rough, and whether there are red areas in it are all checked. If thrush is suspected, a sample from a scraping can be examined under the microscope.

3. 3

   Examination by touch and a neck check

   The NHS writes that the clinician looks at and feels the inside of the mouth, and also checks the neck and under the jaw by hand. Hardness under the patch or a swollen gland in the neck is looked for.

4. 4

   Removing the irritation and waiting 2 weeks

   A sharp edge is smoothed, a filling with a sharp edge is replaced, a denture is adjusted or you are asked to take it out at night; if there is thrush, it is treated. The patch is then checked again. MSD's 2-week threshold sets the timing of this check.

5. 5

   A biopsy for a patch that does not clear

   If the patch has not faded, or looks suspicious at first sight, a small piece is taken and sent to a pathologist. Cleveland Clinic writes that every suspicious leukoplakia should be biopsied and that this is the only way to determine the chance of it turning into cancer. The biopsy is usually done under local anaesthetic in an oral and maxillofacial surgery or oral medicine department.

6. 6

   A plan based on the pathology result

   The report states whether there is disorder in the cells (dysplasia) and, if so, its grade. The meta-analysis found that moderate and severe dysplasia were clearly more associated with turning into cancer than mild dysplasia. The plan takes shape towards monitoring or removal according to this grade and the patch's location and size.

There is no single treatment for a white patch; what is done depends on what the patch is.

The following are the wrong decisions most often seen with this complaint. We set them out so that you can ask the right questions, whichever clinician you see.

The timings vary depending on what the patch is. The sequence below is a general framework; the plan of the clinician who examines you comes first.

1. The first week

   If treatment for thrush has been started, the symptoms are expected to ease. The NHS wants you to see a doctor if there is no improvement after 1 week of mouth gel.

2. The first 2 weeks

   If the source of friction has been removed, the patch is expected to fade. If the patch is still there at the end of the 2 weeks, it is time for a referral for biopsy.

3. After the biopsy

   Ask the clinician who did the biopsy when the result will be ready. The biopsy site heals like a small wound. The plan is made according to the diagnosis and the grade of dysplasia in the pathology report.

4. The long term

   If you have been diagnosed with leukoplakia, regular check-ups continue whether or not the patch has been removed. Cleveland Clinic recommends a check-up every 6 to 12 months for several years.

We are not giving a single figure here, because behind a white patch there may be a few days of thrush treatment, the smoothing of a tooth edge, or a biopsy and surgical removal. These are the items that determine the scope:

What the patch is

Thrush, a friction mark, lichen planus and leukoplakia follow entirely different paths and often fall within the remit of different clinicians.

Whether a biopsy is needed

Taking a sample and the pathology examination are separate items; sometimes samples are needed from more than one area.

Correcting the source of irritation

There is a big difference between polishing an edge and making a new denture.

Length of follow-up

Because check-ups can go on for years after a diagnosis of leukoplakia, the total burden is determined by the follow-up rather than a one-off procedure.