Upper respiratory tract infections are a significant public health problem. Human behavior affects the frequency of contact between infected and susceptible individuals. The seasonality of these infections is related to fluctuations in temperature and absolute humidity, which increases the incidence of respiratory viral infections, especially in winter. Traditionally, cold weather has been thought to make people spend more time indoors, making it easier for cold and flu viruses to spread. However, biological factors contribute to a higher risk of disease in colder environments. Active mucosal defense against bacteria involves the release of antimicrobial extracellular vesicles from the epithelium into the mucus. However, these vesicles weaken significantly when exposed to a cold environment.