Nasal congestion during a cold is a common and often frustrating symptom, yet its underlying mechanisms reveal a complex interplay between the body's immune response and viral infection.

Understanding why the nose clogs during colds requires exploring how viruses trigger inflammation and how this serves both to protect the body and generate the hallmark sensation of blockage.

Viral Infection and Immune Activation

A cold is usually caused by respiratory viruses, with rhinoviruses being the most common culprits. Upon infection, these viruses attach to cells lining the nasal passages and begin replicating. This invasion activates the immune system, prompting nasal epithelial cells to release various pro-inflammatory and vasoactive substances such as cytokines, bradykinins, and prostaglandins.

These chemicals initiate an inflammatory cascade that acts as the body's defense mechanism. They cause dilation of blood vessels in the nasal tissues, increasing blood flow and making the vessels more permeable. As a result, plasma fluid leaks into surrounding tissues beneath the mucosal surface, causing swelling. This swelling narrows the nasal airways and creates the sensation of congestion, effectively blocking or limiting airflow through the nose.

Swelling and Fluid Accumulation

The leakage of fluid into nasal tissues, combined with the influx of immune cells combating the viral infection, contributes substantially to the clogged feeling. The nasal mucosa becomes engorged, and tissues thicken, shrinking the space available for breathing.

This localized edema restricts normal airflow, making it difficult to breathe through the nose. At the same time, the excess fluid may lead to watery nasal discharge, commonly known as a runny nose.

The Nasal Cycle and Temperature Regulation

The nose naturally undergoes a rhythmic pattern known as the nasal cycle, characterized by alternating congestion and decongestion phases in each nasal passage. During a cold, this cycle becomes exaggerated, with one side remaining heavily congested for extended periods. This unilateral obstruction allows for sustained warming of nasal tissues to near core body temperature, approximately 37°C.

Impact on Breathing and Comfort

While nasal congestion plays a protective role, it also significantly impairs normal breathing and comfort. The reduced airflow creates a sensation of stuffiness and can interfere with sleep, concentration, and physical activity. The congestion forces breathing through the mouth, which tends to dry out the airways and throat, sometimes worsening discomfort.

Factors Influencing Severity

The degree of nasal congestion varies depending on viral strain, individual immune response, and other factors such as allergies or preexisting nasal sensitivity. Some people experience more intense inflammation and pronounced blockage, while others have milder symptoms. Environmental factors like dry air or irritants can exacerbate swelling and prolong the congestion phase.

Dr. Gregory Levitin, an otolaryngologist, explains "When someone feels their nose is blocked, this is typically a result of inflammation along the lining of the nose."

Nasal congestion during colds results primarily from the body's immune response to viral infection, which triggers inflammation and fluid accumulation in nasal tissues. This swelling serves both protective and regulatory functions by restricting airflow, raising nasal temperature, and limiting viral replication.

Awareness of these processes enhances appreciation of cold symptoms and informs effective management choices to reduce congestion and support recovery.