Why Does the Nose Run?

A runny nose is something almost everyone experiences from time to time. Whether it happens due to a cold, allergies, or cold weather, it can feel irritating and inconvenient. But why does the nose start running? The answer lies in the body’s defense system. When the nose runs, it is actually a sign that the body is protecting itself. Here’s a detailed explanation of why the nose produces extra fluid – and when you should pay attention.

The Mucous Membranes – The Body’s First Line of Defense

The nasal mucosa is covered with tiny cells that constantly produce mucus. Normally, this mucus helps to:

• Trap dust, bacteria, and viruses

• Moisten and warm inhaled air

• Transport unwanted particles away via small cilia (microscopic hairs)¹

When the mucous membranes are irritated – by infection, allergens, cold air, or chemical substances – mucus production increases to flush away the irritation.

The Most Common Causes of a Runny Nose

Several mechanisms can trigger increased mucus production:

• Viral infections, such as colds and influenza, cause inflammation in the nasal mucosa, leading to a runny nose²

• Allergic reactions, such as hay fever, activate the immune system, releasing histamine and increasing mucus secretion

• Cold air can constrict nasal blood vessels, but also increase mucus production to warm and humidify the air³

• Chemical irritation, like smoke, perfume, or pollution, can trigger reflex-based mucus production

• Physical exertion, for example running in cold air, may cause temporary exercise-induced rhinorrhea

What Does the Type of Mucus Indicate?

The appearance of mucus can provide clues about the cause:

• Clear and thin: typical with viral infections, allergies, or irritation

• Thick and yellow-green: may indicate bacterial infection, especially if persistent or accompanied by fever⁴

• Blood-tinged: may result from irritation or small tears in the mucosa, often due to frequent nose blowing

When Should You See a Doctor?

A runny nose is usually harmless and resolves on its own. But medical advice is recommended if:

• Symptoms last more than 10–14 days without improvement

• You develop high fever, severe facial pain, or swelling

• The mucus remains thick, green, and is accompanied by poor general condition

• It occurs together with severe headache or vision problems

These may indicate sinus infection or another complication requiring medical evaluation.

How to Relieve a Runny Nose

Practical measures that may help include:

• Rinsing the nose with saline to clear irritants

• Using corticosteroid nasal spray for allergic rhinitis (under medical supervision)

• Avoiding known irritants like smoke, strong odors, and cold, dry air

• Maintaining good indoor humidity to protect the mucosa

For most people, a runny nose is a temporary part of the body’s self-healing process and requires no specific treatment.

Sources

1. Eccles, R. (2005). Understanding the symptoms of the common cold and influenza. The Lancet Infectious Diseases.

2. Heikkinen, T., & Järvinen, A. (2003). The common cold. The Lancet.

3. Eccles, R. (1996). Cold-induced rhinitis: mechanisms, diagnosis and treatment. Clinical & Experimental Allergy.

4. Gwaltney, J. M. Jr. (1996). Acute community-acquired sinusitis. Clinical Infectious Diseases.