Allergic rhinitis is a specific IgE mediated inflammatory disease of the nasal mucosa, characterized by symptoms such as rhinorrhea, nasal congestion, nasal obstruction, nasal and eye itching, and sneezing. The prevalence of allergic rhinitis varies according to country, age, and surveying methods, but it seems to increase worldwide, also in Korea. Prolonged mouth breathing caused by allergic rhinitis can produce muscular and postural alterations, causing alterations on the morphology, position, growth direction of the jaws, and malocclusion. Also, mouth breathing leads to dryness of the mouth, causing various oral diseases; gingivitis, halitosis, inflammation of tonsil, increased risk of dental caries and dental erosion. In dental clinic, using rapid maxillary expansion to persistent allergic rhinitis patients with narrow maxilla can enlarge maxillary dental arch and nasal cavity anatomy, improving nasal breathing and reducing nasal cavity resistance. However, it is desirable to use along with otolaryngologic treatment. Dentists should be aware of the characteristics of allergic rhinitis and its effects on patients, and consider when planning dental treatment.