White tongue may be a result of a variety of factors, ranging from poor hygiene to precancerous conditions. The tongue may be inflamed due to dehydration, fever, or smoking, or it may be caused by certain medications. There are also disease conditions that can cause the tongue to appear white, such as thrush or candidiasis, syphilis, or leukoplakia, which may be a precursor to cancer of the mouth. To read more about different causes of white tongue, you can visit here: http://www.mayoclinic.com/health/white-tongue/MY01011/DSECTION=causes
This could indicate fungus and rotting food particles left in your mouth and growing on your tongue. You need to brush you tongue very well if this happens. It can also occur when there is a buildup of bacteria and debris on the surface of the tongue due to mild dehydration, illness (when there is less use of the tongue for talking or eating), or dryness of the mouth and you may even have consult a doctor.
If it's completely white ,I'm sorry.. I can't help ya. If there's a certain area of whiteness it may be something other comments have said ,or if you have some sharp teeth and you can't help but mess with them with your tongue ,it may just be the skin growing back.. I don't know if your tongue could be considered to have skin.. If this doesn't help I'm sorry. But it's just a suggestion because I had a cut up tongue from my teeth being sharp and now it's back to normal.. I think..