The belief that walking in the rain or being exposed to cold air causes a person to become sick is a common idea. However, the scientific reality is that wetness and cold temperatures alone cannot initiate an infection. The connection between cold, damp conditions and the onset of illness is rooted in biological and environmental factors that influence the body’s defenses and the spread of infectious agents. Understanding the true mechanisms of infection and how weather interacts with the body and viruses reveals why this long-held myth persists.
The Actual Cause of Colds and Flu
The sole agents responsible for causing a common cold or influenza are infectious microbes, specifically viruses, not external weather conditions like rain or cold air. The common cold is caused by over 200 different viruses, with rhinoviruses being the most frequent culprit, while influenza is caused by influenza viruses. These pathogens must be contracted through exposure to an infected person or a contaminated surface for sickness to occur.
A person becomes infected when viral particles enter the body, typically through the eyes, nose, or mouth. This usually happens by inhaling airborne droplets from a cough or sneeze or by touching a surface where the virus has landed and then touching one’s face. The water from rain or the sensation of being cold does not create these viruses, nor can it spontaneously generate the disease.
Physiological Effects of Being Cold and Wet
Although wetness does not introduce a pathogen, the body’s response to being chilled can create a temporary state of vulnerability if a virus is already present. When a person is exposed to cold temperatures, the body initiates a defense mechanism called vasoconstriction, which narrows blood vessels, particularly in the extremities and the skin’s surface, to conserve core body heat. This natural reaction shunts warmer blood toward the torso and vital organs.
This physiological response also affects the internal environment of the upper respiratory tract, including the nasal passages, which are the body’s first line of defense against inhaled viruses. Studies have shown that when the temperature inside the nose drops, the local innate immune response can be significantly reduced. This drop in temperature can impair the function of immune cells that are meant to destroy or neutralize incoming viral threats.
Furthermore, the cold air can slow down mucociliary clearance, which is the process where tiny, hair-like structures called cilia sweep mucus and trapped pathogens out of the airways. When this clearance mechanism becomes sluggish, it allows any already-present viruses to remain in the nasal cavity longer, potentially increasing the chance of successful infection and replication.
How Cold Weather Influences Virus Transmission
The primary reason colds and flu are more prevalent in the colder months has less to do with the individual’s direct experience of rain or cold and more to do with population behavior and the physical properties of the viruses themselves. When temperatures drop, people generally spend more time indoors, congregating in closer proximity in spaces with less fresh air circulation. This increased density and lack of ventilation dramatically facilitates the aerosol transmission of respiratory viruses.
The physical characteristics of cold, dry air also play a significant role in viral spread. Low humidity, which often accompanies cold air, allows the respiratory droplets expelled by an infected person to evaporate quickly, leaving behind smaller, lighter viral particles. These smaller aerosols can remain suspended in the air for longer periods and travel farther than larger, heavier droplets.
The combination of the virus thriving in the dry, cold conditions outside the body and people being forced indoors where they are in close contact creates a “perfect storm” for seasonal illness.