Allergic rhinitis is a type of allergy that affects the greatest number of people. It is estimated that from 10 to 30% of people in Japan are affected. Allergic rhinitis, also known as hay fever, is a type of inflammation in the nose which occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose; sneezing; red, itchy, and watery eyes; and swelling around the eyes. The fluid from the nose is usually clear. Symptom onset is often within minutes following exposure. The symptoms can affect sleep, the ability to work, and the ability to concentrate at school. Those whose symptoms are due to pollen typically develop symptoms during specific times of the year. Some people with allergic rhinitis also have asthma, allergic conjunctivitis, or atopic dermatitis. In the Hokkaido area, birch pollen allergy is identified as the cause in 50% of all allergy patients, and 30% of patients allergic to birch pollen have oral and pharyngeal hypersensitivity to fruit such as apples. This is called an oral allergy syndrome (OAS) or pollen food allergy syndrome (PFAS).