Cough

A cough is a sudden, forceful expulsion of air through the large breathing passages. It serves as a vital protective reflex for the body. This reflex helps clear the airways of fluids, irritants, foreign particles, and microbes.

While coughing can be a sign of illness, it is also a natural way for the body to maintain its respiratory health. Because it is a defense mechanism, coughing can become repetitive. If a cough is productive, it means it is bringing up phlegm or mucus. This process is necessary to clean the lungs, so suppressing a productive cough may cause damage.

The biological mechanism of a cough occurs in three distinct phases. First, the body performs an inhalation to bring air into the lungs. Next, the body engages in a forced exhalation against a closed glottis. The glottis is the opening between the vocal cords in the throat. Finally, there is a violent release of air when the glottis opens. This rapid release usually creates a distinctive sound.

This reflex is triggered by the stimulation of two types of nerves in the lungs. These include myelinated rapidly adapting receptors and nonmyelinated C-fibers.

Doctors classify coughs based on their duration. An acute cough lasts for less than three weeks. A subacute cough lasts between three and eight weeks. A chronic cough is defined as lasting longer than eight weeks.

There are also differences in the type of cough produced. A cough can be non-productive, which is a dry cough. A productive cough is one that produces sputum, or phlegm. Some coughs are nocturnal, meaning they occur only at night. Others may be triggered by specific medical conditions or even social reasons, such as a voluntary "ahem" to get attention.

Many different factors can trigger a cough. Most acute coughs, which are shorter than three weeks, are caused by the common cold. Other infections like COVID-19, pneumonia, pertussis, and tuberculosis can also cause coughing. In adults, asthma is a very common cause of chronic cough. Gastroesophageal reflux disease, or GERD, is another major cause. This happens when stomach acid moves up into the esophagus. Some medications, such as ACE inhibitors used for high blood pressure, can cause a cough as a side effect. Even air pollution and tobacco smoke can irritate the respiratory system.

Statistical data shows how much coughing varies between people. A healthy child may cough ten times a day without any disease. A healthy adult coughs an average of 18.6 times per day. However, for people living with respiratory disease, the frequency is much higher. The geometric mean for this group is 275 coughs per day.

In adults with a chronic cough, over 90% of cases are linked to asthma, post-nasal drip, eosinophilic bronchitis, or GERD. These numbers help doctors understand the severity of a patient's condition.

Coughing can sometimes lead to physical complications. Acute complications include cough syncope, which is fainting due to decreased blood flow to the brain. Forceful coughing can also cause vomiting, red eyes from broken blood vessels, or even insomnia. Chronic or violent coughing can lead to more long-term issues. These include abdominal or pelvic hernias and fatigue fractures of the lower ribs. It can also cause costochondritis, which is inflammation of the cartilage in the chest. In some cases, chronic coughing can damage the pelvic floor.

From a public health perspective, coughing is a major way that diseases spread. Many viruses and bacteria have evolved to cause coughing in their hosts. This helps the microbes travel to new people through infectious droplets.

To reduce this spread, people can cough into their elbow or toward the ground. This is safer than coughing forward at breathing height. Using masks, such as surgical masks or N95 masks, can also help control the movement of these droplets in the air.