A white tongue can occur due to the invasion of fungi or bacteria on the tongue surface. This causes dead cells to be trapped within the nodules of the tongue.
There is no cause for concern since a white tongue is usually not a medical condition, but a temporary issue. Drinking plenty of water and brushing the tongue with a scraper can help remove the white coating. However, if the coating is associated with an infection, it is sensible to seek medical attention. Conditions that can cause a white tongue include syphilis, oral lichen planus, oral thrush and leukoplakia, as stated by NHS.