Although it is a very common phenomenon, many people don’t really know why it’s easier to catch a cold, the flu, or COVID in the winter. It is clearly known that being cold won’t give you a cold. Then why does the spread of so many respiratory viruses peak during winter?
This wintertime seasonality has puzzled common people and scientists alike for a very long time, thousands of years. Evidence suggests winter’s shorter days coupled with less sunlight, less activity and more indoor times may make people more susceptible to infection. One of the reasons for this is the diminished synthesis of vitamin D, which is required for better immune responses.
Also, when we live in proximity to each other for a longer time in an indoor environment, the aerosols containing pathogens can build up making individuals more contagious, and facilitating the transmission. While dryer air can give some viruses a boost, it is known to tear down people’s defenses against viruses. Animal studies have shown that dry air can trigger the death of some cells in the airway lining, leaving cracks for viral invasion. Also, studies have shown that the altered relative humidity directly affects the formation of airborne droplets and viral transmission.