The common cold is an infection of the upper respiratory tract caused by viruses, primarily rhinoviruses. These viral infections are responsible for familiar symptoms like a runny nose, sneezing, and sore throat. Despite the long-held belief that exposure to cold air or a draft can make a person sick, the illness is not caused by temperature alone. This misconception ignores the fundamental role of infectious agents.
Separating Temperature from Infection
Colds are more common during colder months due to changes in human behavior and the environment, not temperature itself. Colds are caused by one of over 200 types of viruses that attack the respiratory system. The peak of cold season correlates with people spending more time indoors in close proximity, which facilitates virus transmission between individuals.
The cold environment also affects the virus and our body’s defenses. Rhinovirus, the most common cold virus, reproduces more efficiently at the cooler temperatures found inside the nasal passages. Additionally, the low humidity common in heated indoor spaces during winter can impair the body’s natural defense mechanisms. Dry air causes the cilia in the nose to become less effective at sweeping away trapped viruses and mucus, reducing our primary line of defense against infection. The increased winter prevalence results from increased indoor crowding, drier air, and a biological advantage for the virus.
Ventilation and Viral Transmission
The concept of “fresh air” is relevant for preventing viral spread in shared indoor environments. Cold viruses spread through respiratory droplets and aerosols released when an infected person talks, coughs, or sneezes. While larger droplets fall quickly, smaller aerosols containing the virus may remain suspended in the air for minutes to hours.
In enclosed spaces with poor ventilation, these viral particles accumulate, increasing the concentration of the virus and raising the risk of transmission. Introducing fresh air, such as by opening a window, creates an air exchange that dilutes the infectious aerosols. This dilution lowers the overall viral load in the room, reducing the likelihood that a susceptible person will inhale enough virus to become infected. Opening windows for even short periods improves airflow and helps manage the concentration of airborne respiratory pathogens.
Managing Symptoms Through Air Moisture
While ventilation addresses transmission risk, the moisture content of the air plays a role in managing cold symptoms. Many indoor environments, especially those heated during the winter, feature low relative humidity. This lack of moisture directly irritates the nasal passages and throat, which are already inflamed by the cold virus.
Dry air causes the mucus membranes lining the respiratory tract to dry out, making the mucus thicker and more difficult to clear. This dryness can lead to a scratchy throat, coughing, and increased congestion. Increasing the air moisture, often through a clean humidifier, helps to soothe these irritated airways. The added humidity keeps the nasal linings moist and thins the mucus, making it easier for the body’s natural clearance mechanisms to function. Maintaining an indoor humidity level between 30 and 50 percent is often recommended to alleviate cold symptoms and provide respiratory comfort during recovery.