Why do colds leave some people feeling awful, while others barely feel sick? New research indicates that this difference may come from the nose and its early immune defenses, which can stop a virus before symptoms begin. The common cold is primarily caused by rhinovirus, a contagious infection that affects the upper respiratory tract, including the linings of the nose, throat, sinuses, and trachea. But scientists believe the virus itself does not determine the severity of the cold. Instead, the intensity is shaped by the speed and strength of your body’s initial response.

A research team at Yale School of Medicine began investigating this theory by culturing lab-grown human tissue using nasal stem cells. For four weeks, the tissue was exposed to air to promote maturity into a structure that strongly mirrors the lining of the nose and lungs, with mucus-producing cells and cells with cilia, tiny hairs that help transport mucus and other particles out of the respiratory tract. Using these creations, the scientists could see how thousands of human nasal cells respond to rhinovirus. As rhinovirus does not infect any animals other than humans, making this model was key for studying the virus and its replication.

Upon detection of rhinovirus, the cell releases interferons, which activate antiviral defense in both infected cells and nearby healthy cells, making it more difficult for the virus to replicate in the body. If the interferons reacted quickly, the virus struggled to multiply, and the infection was contained. On the other hand, when the scientists intentionally blocked interferons from being produced, the virus spread extremely quickly, greatly damaging many cells and even destroying the tissue entirely in some cases. The timing of the nose’s defense system largely dictates how intense the infection becomes before the immune system attacks.

The researchers also found that when the virus becomes more widespread, it can activate additional cellular pathways that increase mucus production and inflammation. This contributes to the typical symptoms of the common cold, such as congestion and difficulty breathing. These reactions are often much more severe in people with asthma or other chronic respiratory conditions.

However, the scientists highlighted that their lab-grown tissue does not fully mimic the conditions found in the human body. In true human infections, many other cells, such as immune cells, are rushed to the nose and airways to help limit the spread of the virus. Future research is imperative to learn how exposure to previous infections and environmental factors influences the body’s reaction to rhinovirus and its severity.

Nonetheless, this study supports the idea that the body’s reaction may influence the infection more than the virus itself. By looking into the body’s early defense responses, scientists aspire to find discoveries that strengthen this reaction while minimizing harm. Understanding how nasal cells engage with rhinovirus could lead to improved methods to reduce and treat the common cold.