Clear fluid dribbling from the nose, usually caused by inflammation of the nasal mucous membrane. A typical symptom of a cold, troublesome catarrh can also be a side-effect of hay fever. The nasal mucous membrane contains many mucus-producing cells. When the membrane is stimulated by a virus or by pollen in the case of hay fever, the cells produce mucus of a watery consistency, and when this happens in quantity it causes a runny nose. When the cause is a virus, such as a cold, the nose will dry up again in a few days to a week, but in the case of hay fever the runniness may persist for as long as there is pollen in the air in large quantities. In serious cases the doctor may provide anti-allergy treatment, to relieve the nose, and ordinary nasal drops can give some relief, even if the nose is not blocked. The drops cause narrowing of the small nasal blood vessels, thus preventing the production of too much mucus. Such treatment should be used only for three or four days, to avoid damaging the mucous membrane. In general catarrh is not a serious condition, and should clear up in a short time, but in some cases there can be associated bacterial infection. The nasal fluid becomes greenish in colour, and thicker, and if there is associated headache, then sinusitis could have set in.