I think it could be bacteria building up on your tongue from not keeping your mouth clean enough. It could also be from not ingesting enough water and your toung is showing signs of dehydration. I became dehydrated once and my tongue turned whitish as well. I'm also a smoker and the smoke we inhale may also contribute to making you have a white tongue b/c of the harshness of the smoke coasting over our tongue everytime we inhale.