Runny nose or rhinorrhoea is a commonly experienced symptom of the common cold and flu, as well as allergic rhinitis. The discharge may be thin, clear and watery but can change to a thick green or yellow coloured, purulent one. This suggests a secondary infection.
Nasal congestion occurs because of dilation of blood vessels, leading to swelling of the surface lining of the nose. This narrows the nasal passages which are further blocked by increased mucous production. Rhinitis is classified into allergic rhinitis (seasonal or perennial), infectious rhinitis, idiopathic rhinitis and rhinitis medicamentosa. It is important to be able to distinguish between these types of rhinitis because optimal treatment depends on accurate diagnosis.