Causes of runny nose, also called rhinorrhoea may include:

 

Allergic Rhinitis: Inhalant allergy

Food Allergy

Non-Allergic Rhinitis

Environment such as cold weather, air conditioning, dry air etc

Common cold

Sinusitis, acute and chronic

Foods, such as spicy food

Certain medications

Hormonal changes

Smoking

Often the symptom of running nose is accompanied by other associated symptoms such as nasal itchiness, stuffiness, obstruction or even bleeding.

A detailed history and examination, including nasal endoscopy may be necessary to make a diagnosis.

Other investigations such imaging studies and allergy tests may be required.