White coat on the tongue does not cause pain but still, it is a serious condition. Oral thrush is a term often used for white coated tongue in the dentistry. If you are suffering from the same problem then you should take it into considerations. In severe cases, your tongue may appear very hairy like covered with white furs. And it also causes your mouth to smell fouled 
Causes of the white coated tongue:

*The excess growth of a fungal infection called “Candida” which is present in various parts of our body results in white coated tongue
*People with the weak immune system more often come across this dental problem
*Excess usage of tobacco may also lead to white coated tongue
*A white tongue may also be the result of some inflammatory disorders like geographic tongue and oral lichen planus
*Bacterial and oral viral infections like Candida, Herpetic stomatitis, or *Hairy Leukoplakia are the common causes of white tongue
*Biting of the tongue, acidic burning sensation in the tongue, misalignment of teeth or cuts and cracks around the tongue also results in white tongue
*HIV infection and oral cancer are the important causes of white tongue
*Negligence to oral care also results in forming dead skin cells on the surface of the tongue which in turn results in white tongue
*During summer when the temperature is too high, consuming less water leads to dehydration which in turn causes a white tongue
*If you breathe from the mouth, it leads to dry mouth or tongue due to which white layers are formed on the upper surface of the tongue
*Excess intake of alcoholic beverages causes several imbalances in the mouth which in turn results in whitening of the tongue
*Excess growth of tissues around the tongue also leads to the formation of white layers on the tongue