Yeast is a type of fungus that can also grow in plaque, especially if you have a high-sugar diet or a dry mouth. Yeast can help bacteria grow by providing them with oxygen-free zones where they can thrive. Yeast can also cause infections like thrush or oral candidiasis, which is a white coating on your tongue or inner cheeks that can be painful or itchy. Yeast and bacteria stick to each other and to the tooth surface, forming a protective layer that shields them from saliva, brushing, and antimicrobial agents. This layer is called a biofilm, and it makes the plaque more resistant to removal.