Hay fever, also called allergic rhinitis, is an allergic inflammation of the nasal airways. It occurs when an allergen, such as pollen, dust mites, mould or animal hair is inhaled by an individual with a sensitized immune system. It is common in spring because it is often caused by an allergy to grass pollen. Hay fever can occur at any time of the year. This is known as perennial allergic rhinitis. Symptoms include a running nose, sneezing and itchy, watering eyes. The most effective way to control hay fever is to avoid exposure to the allergen (if identified), but this is not always possible. Medication including corticosteroid nasal sprays, antihistamines and staying indoors can help symptoms. Allergen immunotherapy may be a suitable treatment for some people.