Geographic tongue is a common condition that causes a characteristic appearance, which experts recognise instantly. The tops of the tongue, sides and occasionally, undersurface of the tongue develop irregular, smooth red areas, which may look like the outline of a map. There are usually wavy white lines next to the red patches.You may notice that after a few weeks or months the position of these lines and red patches change. This is why the condition is called erythema migrans in Latin, as its position changes and moves.
For reasons as yet not understood, the normal top layer of the 'skin' of the tongue is not shed evenly. In some parts the 'skin' is shed too early and so leaves a red, sore area like a scratch on the skin. Whereas in other areas the skin stays on too long and has a white appearance.The red areas, because they are thin, can sometimes become infected with thrush (candida) and so feel sore. Thrush is very common in mouths.
Unfortunately, there is no treatment. Sometimes treatments for thrush can ease the discomfort. You can buy these at the chemist, eg miconazole gel. It will never become cancerous, but you will have to learn to live with it. You will need to work out for yourself which foods make it worse and avoid them.