Rhinitis, commonly known as a runny nose, is the medical term describing irritation and inflammation of some internal areas of the nose. Rhinitis is very common. Allergic rhinitis is more common in some countries than others; in the United States, about 10%–30% of adults are affected annually. Allergic rhinitis, often called allergies or hay fever, occurs when your immune system overreacts to particles in the air to which you are allergic. Nonallergic rhinitis is a medical term that describes a set of symptoms that resemble an allergy but that occur without a known cause.