The human respiratory system has its own defense mechanisms that help the body resist viruses responsible for the common cold.

A new study published in Cell Press Blue has shown that the nasal passages play a much more active role in the first line of defense than previously thought. Researchers found that the nasal cavity acts not only as a filter for particles and microbes but also as a site where the immune response is triggered, potentially stopping viruses before they spread deeper into the respiratory tract.

The study involved volunteers who were given small doses of viruses similar to those that cause the common cold through the nose. Scientists monitored changes in mucus, epithelial cells, and immune system molecules present in the nasal cavity. They discovered that in the early stages of infection, numerous protective molecules and proteins are activated, interfering with viral replication and preventing the virus from moving further into the body. This includes interferons—special proteins produced by cells to suppress viruses—as well as other immune signaling molecules.

One of the key findings was that the immune response in the nasal passages can be specific to different viruses. This means that cells in the mucous membrane are able to “recognize” certain pathogens and rapidly activate the molecules that are most effective against them. This localized response acts as a barrier, preventing the infection from spreading to the lungs and other parts of the respiratory system.

The authors note that this may be one reason why some people experience milder colds or even no symptoms at all despite exposure to a virus. A strong local immune response in the nasal cavity can limit viral replication at an early stage and stop the infection from developing into a more severe illness.

These findings also help explain why common nasal hygiene practices—such as rinsing with saline solution—may reduce the likelihood of developing symptoms or lessen their severity: clearing the nasal passages helps remove some of the viruses and supports optimal conditions for local defense mechanisms to function.