The stratified squamous epithelium of the oral mucosa is characterized by significant regional variations mainly with regard to differences in the degree of keratinization. The oral mucosa is also divided into lining, masticatory, and specialized types reflecting the functions in different areas. The permeability barrier in the oral mucosa is mainly a result of membrane-coating granules composed of various lipids that differs between nonkeratinized and keratinized regions of the oral mucosa. Another feature of the environment of the oral cavity is saliva, which contains mucins that lubricate and protect the oral mucosa. Filaggrin is believed to function as a matrix protein supporting the aggregation of keratin filaments, and it has been demonstrated in especially keratinized oral mucosa like the palate. Filaggrin and its metabolites may contribute to difference in the functions and properties of the oral epithelia. Likewise, filaggrin gene (FLG) mutations and altered distribution of filaggrin/profilaggrin in oral mucosa may play a role in disorders affecting the oral epithelia, including oral contact allergy.