Sometimes, white coating may be due to the accumulation of dead skin cells. Just like any other part of your body, the skin on your tongue also sheds every few days. If the dead cells go on accumulating on your tongue, eventually you begin to notice white spots on your tongue. At times, dehydration may result in the formation of a white coat on the tongue. If you constantly feel thirsty, then dehydration may be the cause behind your problem.