The membranes of the nose and mucosa of the sinuses produce a litre of mucus each day. Mucus plays a fundamental role in the respiratory system: it helps purify, moisten and heat inspired air while trapping particles such as bacteria and dust from the environment. Under normal conditions, mucus is ingested and the stomach acid destroys the particles and bacteria trapped in it.
What is runny nose or rhinorrhea?
Nasal discharge or runny nose (rhinorrhea) occurs when the mucous membranes produce an excess of mucus that either drains through the nose or builds up in the throat.
What causes a runny nose?
There are several causes for a nasal discharge: the common cold, flu, rhinitis, and sinusitis are the most frequent.
Depending on the cause, the duration of nasal discharge may vary. In the case of a cold or flu, the runny nose usually lasts about 5–7 days. If it lasts more than 10 days, rhinosinusitis is likely the cause.
The classic symptoms of sinusitis, in addition to a runny nose, are nasal congestion, facial pain or pressure, and reduction or loss of the sense of smell. These symptoms are because the excess mucus produced gets trapped inside the sinuses and presses on their walls. Since the problem is the accumulation of mucus, the solution is to drain them. This seems easy but it is not, as the anatomical location and physiology of the sinuses makes it difficult for nasal sprays to reach and act on them.