Why Do We Always Get Cold Or Flu In Cold Weather?

The common cold and flu are often associated with cold weather. According to the Centers for Disease Control and Prevention (CDC), millions of people develop it each year. On average, adults have two or three colds per year. Colds can be caused by a variety of viruses [1].

A study published in the Journal of Allergy and Clinical Immunology describes a mechanism in the nose which could explain the increased susceptibility to upper respiratory infections during the winter months [2].

Why Do We Always Get Cold Or Flu In Cold Weather?

Here are the important points from the study:

Point 1: One of the components of the immune response against respiratory viruses involves the release of swarms of membrane-bound particles called extracellular vesicles (EVs) by cells that line the nasal cavity.

Extracellular vesicles (EVs) are nano-sized lipid bilayer vesicles released by virtually every cell type. EVs have diverse biological activities, ranging from roles in development and homeostasis to cancer progression, which has spurred the development of EVs as disease biomarkers and drug nanovehicles [3].

Point 2: In the nose, EVs can prevent viruses from binding to uninfected cells or transferring their cargo to uninfected cells and modulating their immune response.

Point 3: In the current study, winter-like temperatures resulted in lower temperatures - from 37 degrees Celsius to 32 degrees Celsius - in the nasal cavity, which weakened this immune response.

This 5-degree drop in temperature inside the nasal cavity attenuated the release of EVs and the antiviral response mediated by these EVs, explaining the increased susceptibility to common colds in winter.

Point 4: This drop significantly reduced this innate immune response in the nose, decreasing not only the quantity of extracellular vesicles that swarmed the virus but the quality of them. This reduced response can make the virus more able to both stick to and then infect the nasal cells, where they can then divide and cause the infection - resulting in cold and flu in winter or colder months [4].

Point 5: Also, by activating toll-like receptors in the nose, EVs are released, which trigger a defensive response in response to the cold-causing bacteria. However, in addition to carrying proteins that can bind microbes and neutralise them, these EVs can also donate enhance the immune response.

Point 6: Recent studies suggest that cold temperatures can reduce the immune response that is evoked by the upper respiratory tract to these viruses, increasing the susceptibility to infection. Due to its proximity to the external environment, the nasal cavity is more sensitive to changes in ambient temperature than the rest of the body, including the lungs.

On A Final Note...

Researchers believe that these findings represent a first genuine mechanistic, biological explanation for why colds and other viruses that cause upper respiratory infections are more prevalent in cooler temperatures.