Allergic rhinitis is a medical condition which is characterized by the overactive immune response of the body to certain tiny particles in air called allergens. When a person inhales these allergens through nose or mouth, the immune system of the body produces a chemical called histamine in increased amounts. This chemical is responsible for an allergic response of the body. The common symptoms include nasal congestion, frequent sneezing, irritation of nose or throat, etc. It is commonly known as common cold.