By far the most common cause for nose discharge (or a runny nose) is a viral infection such as common cold or influenza, or a bacterial infection such as sinusitis. Viral infections usually have a lightly colored discharge, but in bacterial infections the patient is sicker with a fever, face ache and green or dark yellow discharge.
Hay fever (allergic rhinitis) is the next most common cause. The discharge is watery and profuse, and sneezing may be almost continuous, but the patient is otherwise well. Almost any substance (eg. pollens, dust, chemicals) may be inhaled and cause this reaction in a sensitive individual.
Vasomotor rhinitis is a reaction of the moist lining in the nose to a change in temperature (e.g. walking into an air-conditioned room), position (e.g. lying down), eating hot or cold food, or drinking (particularly alcohol) that results in the production of copious amounts of watery mucus. The problem usually settles after ten to thirty minutes, unless there is a further irritation of the nostril.
Children often place objects in the nose and they may be difficult to see without proper instruments. A foreign body may be the cause of a nasal discharge, which is often infected, in children and adults with subnormal mentality.