Geographic tongue is a harmless condition affecting the top surface of the tongue. The appearance of the tongue, with the wavy outline of the affected areas, supposedly resembles the coastline on a map. The other name for it is erythema migrans: ‘erythema’ for the redness of the patches, and ‘migrans’ for the fact that the areas affected seem to migrate, or move, over the surface of the tongue. The condition is not very common (about 2 per cent of the population), and may only affect a person for a short time before disappearing of its own accord.

The pattern seen on the surface of the tongue, that of white and red patches with wavy margins, reflects the different thickness of the protective surface of the tongue in different places. In some areas of the tongue, the protective covering is thinner than normal, so the tongue appears redder. In other, paler areas, and especially at the junction between a pink and a white area, the surface covering of the tongue is thicker than usual.

The cause is unknown, though the condition does appear to run in families. Geographic tongue is not an infection, so the condition cannot be caught or passed on. The different appearances are normal when looked at down a microscope, and do not represent disease or cancer.

For some people the change in the appearance of the tongue is the only thing to note. In others, the tongue becomes a little more sensitive, especially to spicy foods or acidic substances such as citrus fruits or vinegar.

No treatments are available which will cure the condition. Some medications can be bought over the counter in a pharmacy that can lessen any discomfort. For example:

Corsodyl mouthwash – an antiseptic mouthwash which helps to keep the mouth clean and reduce inflammation Difflam – a mouthwash or spray which can temporarily numb the lining of the mouth and reduce its soreness.