The common cold is a mild, contagious viral infection affecting the upper respiratory tract, including the nose and throat. The viruses that cause the cold are highly transmissible. This ubiquitous illness is responsible for more missed days of school and work than any other infection each year. Understanding how this infection is caused and transmitted is the first step in protecting others.
The Agents of Infection
The common cold is exclusively caused by viruses, not by exposure to cold weather or bacteria. Over 200 different viral strains can trigger cold symptoms, explaining why people catch colds repeatedly. The most frequent culprits are Rhinoviruses, which account for the majority of common colds.
Other viral families, including certain Coronaviruses, Adenoviruses, and Parainfluenza viruses, also cause cold-like illnesses. Because immunity is specific to the strain a person encounters, the sheer number of circulating viruses means a person is rarely immune to all threats.
How Colds Spread
Cold viruses move from an infected person to a healthy one through several primary mechanisms. The first is the transmission of respiratory droplets released when a person coughs, sneezes, or talks. These virus-containing droplets can be inhaled directly by individuals in close proximity, leading to infection.
Another common pathway is direct physical contact, such as shaking hands with someone who has the virus on their skin. An infected person often transfers the virus to their hands when they cough or wipe their nose. The virus is transferred when they touch another person, entering the body when the recipient touches their own mouth, nose, or eyes.
The third method involves fomites, which are contaminated surfaces or objects. Cold viruses can survive on hard surfaces like doorknobs, countertops, and phones for hours. Touching a contaminated object and then touching a mucous membrane of the face—the eyes, nose, or mouth—provides a direct entry point for the virus.
When You Are Most Contagious
A person becomes contagious before symptoms even begin, during the incubation period when the virus is multiplying inside the body. This period usually lasts between one and three days after initial exposure. You can unknowingly spread the virus to others during this time, often one to two days before feeling sick.
Infectiousness peaks during the first two to four days after symptoms appear, when nasal discharge and coughing are at their worst. High levels of the virus are shed during this initial phase. Although the cold virus can continue to spread until symptoms resolve, the risk of transmission decreases significantly after the first week.
Stopping the Spread
Preventing the spread of a cold relies on rigorous hygiene practices. Frequent handwashing is the most effective method, and it should be done with soap and water for a minimum of 20 seconds. If soap and water are not available, using an alcohol-based hand sanitizer with at least 60% alcohol can reduce the viral load on the hands.
Respiratory etiquette is also important, meaning covering coughs and sneezes to contain virus-laden droplets. The recommended practice is to cough or sneeze into a tissue and immediately dispose of it, or to use the upper sleeve or elbow if a tissue is unavailable. This prevents the virus from landing on hands or being sprayed into the air and onto surfaces.
When a person is ill, limiting close contact with others reduces transmission. This involves staying home from work or school during the most contagious period and maintaining physical distance from people who are not sick. Regularly cleaning and disinfecting frequently touched surfaces, like light switches and remote controls, also helps eliminate viral particles.