Many people across cultures have grown up believing that cold temperatures directly cause illness. The idea that going outside without a coat, breathing frigid air, or simply feeling chilled leads to colds or the flu is remarkably common. But modern research reveals a far more nuanced relationship between temperature and infection.
Why You Don’t “Catch a Cold” From the Cold
The common belief that cold weather makes you sick isn’t quite accurate—it’s more about how cold affects viruses and your body’s defenses.
Low temperatures alone don’t cause infections. Instead, they influence a complex interplay of biological, environmental, and social factors that increase vulnerability to respiratory illnesses, particularly during winter. Colds and the flu are caused by viruses—rhinoviruses for the common cold and influenza viruses for the flu—which spread from person to person through respiratory droplets or physical contact, regardless of the outside temperature.
However, respiratory infection rates consistently rise during colder seasons globally. This pattern is partly due to how low temperatures and low humidity impact viruses in the environment. Research shows that many respiratory viruses, including influenza viruses and coronaviruses, survive longer and remain infectious for extended periods in cold, dry conditions.
Dry air also causes the tiny droplets released when breathing, talking, coughing, or sneezing to evaporate rapidly. This creates smaller particles that linger in the air longer, increasing the likelihood of inhalation by others. Consequently, cold, dry air helps viruses persist and enhances their chances of reaching another person’s respiratory system.
Cold air also impacts the body’s defense mechanisms. Breathing cold air lowers the temperature inside the nose and airways, triggering vasoconstriction—the narrowing of blood vessels, which reduces blood flow to tissues. This decreased blood flow in the nasal and airway lining can weaken local immune responses that normally detect and eliminate viruses before they cause infection. Cold exposure and related stress can also disrupt normal airway function, particularly in individuals with sensitive respiratory systems, suppressing the body’s initial defenses.
The Role of Crowds and Close Contact
Seasonal shifts in human behavior and indoor environments also play a significant role. Cold weather drives people indoors, often into close proximity with one another. Crowded, poorly ventilated spaces allow virus-containing droplets to accumulate, facilitating transmission. During winter, reduced sunlight exposure lowers vitamin D production in the skin. Vitamin D regulates immune function, and low levels are linked to weaker immune responses.
Indoor heating, while providing comfort, dries out the air. This dryness can impair the lining of the nose and throat, reducing the effectiveness of mucus—which normally traps and expels viruses through mucociliary clearance. When this system is compromised, viruses find it easier to infect cells.
The evidence paints a clear picture: low temperatures are associated with higher rates of respiratory infections, including flu and coronaviruses, especially in temperate regions during winter. Laboratory and environmental studies demonstrate that viruses survive longer and spread more easily in cold, dry air. Cold exposure can also weaken immune defenses in the nose and airways, reducing mucus mobility and antiviral activity. Behavioral and environmental factors—indoor crowding, poor ventilation, and reduced vitamin D levels—further elevate the risk of viral spread.
However, the evidence does not support the idea that simply being cold—like going outside without a coat—directly causes a cold or flu. Instead, cold acts as a risk amplifier, creating conditions that help viruses survive, spread, and overcome the body’s defenses.
Understanding this distinction is practical. Improving indoor ventilation and maintaining adequate humidity during winter can reduce transmission risk. Supporting immune health, including maintaining sufficient vitamin D levels, is also beneficial.
Public health messaging is most effective when it focuses on how viruses spread through contact and respiratory droplets, rather than perpetuating the myth that cold alone causes illness.
In short, cold weather and illness are related, but not as many assume. Low temperatures don’t independently cause infections; they shape the biological, environmental, and social conditions that allow respiratory viruses to thrive. Recognizing this complexity explains why colds and flu peak in winter and supports more effective prevention strategies, dismantling a simple but misleading belief.
