Rhinorrhoea is the symptom described by the layperson as a runny nose. The main constituent of nasal fluid is water (96-97%) but it also contains mucin (2.5-3%) and electrolytes (1-2%).
The colour of the nasal discharge may give a clue as to its cause:
- clear - normal or allergy
- green - active nasal infection; discolouration is due to the enzyme verdoperoxidase released from dead leucocytes
- yellow - indicates a raised protein content; sometimes seen in allergic disorders that are not complicated by secondary infection