A cough is a forceful, involuntary reflex action designed to protect the airways. This mechanism expels air from the lungs, throat, and mouth, clearing foreign substances, irritants, excess mucus, and pathogens from the respiratory tract. While the cough itself is merely a symptom, it is the primary vehicle for spreading the underlying infection. Determining if a cough poses a risk to others depends entirely on whether its root cause is an infectious agent, such as a virus or bacteria, or a non-infectious irritant.
How Respiratory Illnesses Spread
When an infected person coughs, they propel infectious particles into the surrounding environment through three primary mechanisms of transmission. The cough generates respiratory secretions of different sizes, dictating how far the particles travel. Larger respiratory particles, known as droplets, typically fall quickly onto surfaces within a short distance, generally within six feet of the source. These virus-laden droplets can infect others when they land directly on the mucous membranes of the eyes, nose, or mouth.
Smaller, microscopic particles, referred to as aerosols, are light enough to remain suspended in the air for extended periods. These particles can travel beyond the short-range droplet zone, allowing for transmission over longer distances, especially in poorly ventilated indoor spaces. The third mechanism involves fomites, which are contaminated surfaces where infectious particles have settled. If a person touches a contaminated surface and then touches their own face, the pathogen can be transferred, leading to infection.
Common Contagious Causes of Coughing
The most frequent causes of a contagious cough are viruses that target the upper and lower respiratory tracts. The common cold is highly contagious, with peak infectivity occurring during the first two to three days of symptoms. Though symptoms can last up to two weeks, the virus is often shed for the entire duration of the illness. Influenza, commonly known as the flu, is also highly transmissible, with individuals able to spread the virus starting about one day before symptoms appear and continuing for five to seven days after the illness begins. The period of highest contagion for influenza is concentrated within the first three to four days of feeling sick.
COVID-19, caused by the SARS-CoV-2 virus, spreads easily through coughing and respiratory activities. The infectious period often begins one to two days before symptoms are noticeable and is typically most transmissible around the fourth day of illness. The virus can remain contagious for eight to ten days after symptoms first begin, though people with compromised immune systems may shed the virus for longer periods. Less commonly, a cough can be caused by bacteria, such as the Bordetella pertussis bacterium responsible for pertussis, or whooping cough. This highly contagious bacterial infection is characterized by severe, uncontrolled coughing fits and remains infectious until about three weeks into the paroxysms, or until a course of antibiotics is completed.
When a Cough Is Not Contagious
Many common causes of coughing are not infectious and therefore pose no risk of transmission to others. These non-contagious coughs are typically the result of irritation, inflammation, or a mechanical issue within the respiratory system. One frequent non-infectious cause is irritation from environmental factors like seasonal allergies, which trigger a cough reflex due to exposure to pollen, dust, or mold. Similarly, exposure to environmental irritants like strong chemical fumes, air pollution, or tobacco smoke can directly stimulate the cough receptors in the airways without involving a pathogen.
Asthma causes a cough because the airways become inflamed and narrowed, often leading to a chronic, dry cough that can be triggered by exercise, cold air, or allergens. Gastroesophageal Reflux Disease (GERD) is another frequent cause, where stomach acid travels up the esophagus and irritates the throat and respiratory tract, triggering a chronic cough, particularly when lying down. Certain medications can also induce a persistent, non-productive cough, most notably Angiotensin-Converting Enzyme (ACE) inhibitors, used to treat high blood pressure. This occurs because the medication sensitizes the cough reflex, a mechanism unrelated to viral or bacterial spread.
Stopping the Spread of Coughs
Preventing the spread of a contagious cough relies on a combination of personal hygiene practices and environmental awareness. The most direct strategy is maintaining proper respiratory etiquette, which involves covering the mouth and nose completely during a cough or sneeze. The preferred method is to use a disposable tissue, which should be immediately thrown into a waste receptacle, or to cough into the upper sleeve or elbow if a tissue is not immediately available. Coughing into the hands should be avoided, as this transfers pathogens directly to surfaces and other people upon contact.
Hand hygiene is a foundational defense, requiring frequent washing with soap and water for at least 20 seconds, especially after coughing, sneezing, or touching shared surfaces. If soap and water are unavailable, an alcohol-based hand sanitizer containing at least 60% alcohol can be used as an alternative. The use of source control, such as wearing a well-fitting face mask, is highly effective for individuals who are coughing, as it contains infectious respiratory particles and reduces their expulsion into the air. Additionally, improving ventilation by opening windows or using air filtration systems can help disperse and remove virus-laden aerosols from indoor spaces, especially when an infected person is present.