Runny nose

Runny nose (Rhinitis): Why does it flow from the nose?

Runny nose, or rhinitis, is inflammation of the nasal cavity's mucous membrane, accompanied by one or more symptoms: nasal congestion, discharge (rhinorrhea), sneezing and itching. It is an extremely common condition, which in most cases is a manifestation of a common cold, but can also have other non‑infectious causes, such as allergies. The mucus produced during a runny nose is an important protective mechanism.

Physiology of mucus production

The nasal mucosa functions as a "conditioner": it warms, humidifies and cleans the air we breathe. It is covered with cup‑shaped cells that continuously produce a small amount of mucus. This mucus traps dust, microbes and other particles. When a virus or allergen reaches the mucosa, the body initiates an inflammatory response: blood vessels dilate, and cells begin to produce significantly more mucus to mechanically "wash away" the irritant.

Infectious vs. Allergic rhinitis

• Infectious rhinitis (URI): The most common cause. Caused by viruses. Initially, discharge is usually clear and watery. After a few days, when immune cells (neutrophils) join the fight, the mucus can become thicker and take on a white, yellow or greenish colour. Color change is not a sign of bacterial infection and does not require antibiotics.
• Allergic rhinitis: Occurs in response to allergens. If it is seasonal allergy, the cause is pollen; if perennial – house dust mites, animal hair. Allergic rhinitis is characterized by bouts of sneezing, copious clear watery discharge and intense itching in the nose and eyes.

Drainage of mucus down the back wall of the throat (post‑nasal drip) is a common cause of cough and sore throat. In pregnant women a runny nose can have a hormonal nature, as discussed in the article "Nasal congestion during pregnancy".