A cough is a sudden and strong release of air from the lungs. It is not an illness, but a protective reflex designed to help you clear foreign material or excess secretions, such as mucus, from your airways.
Coughs are often categorized based on two characteristics—whether or not they produce or expel mucus, and how long they last. A productive cough is one that produces or expels sputum (also known as mucus or phlegm). Productive coughs help clear and protect the lungs and other parts of the lower respiratory tract from infectious mucus and other potentially harmful agents. Nonproductive, or “dry” coughs, produce little or no sputum; they are usually the result of a minor irritation in the throat.
A cough can be very brief, lasting just long enough to clear something from your throat. Or it can last for several days, weeks, or even months. An acute cough is one that lasts for less than three weeks. A chronic cough persists for more than three weeks. Acute coughs can become chronic.
An estimated 14% to 23% of non-smoking adults have a chronic cough, which is why coughing is the fifth most common reason people visit their doctor. Among smokers, the incidence of chronic cough is even higher: Approximately 25% of people who smoke one-half pack per day and 50% who smoke more than two packs per day report having a chronic cough.
Coughing is an automatic reflex that begins when your body senses that something has entered your airways that shouldn't be there. Nerves called cough receptors, which are located near the surface of the upper and lower passages of the respiratory tract, sense the presence of the unwanted material and send distress signals to your brain. The brain then relays messages to your lungs and respiratory muscles, which force you first to take a deep breath and then to exhale forcefully.
The force behind a cough occurs because the opening to your windpipe (the glottis), located at the back of your throat, momentarily closes as you exhale. While the glottis is closed, extra pressure builds up in your lungs. Then, when the glottis finally opens, the air explodes out, helping to dislodge particles from your airways.
Some structures located near the airways, such as the pericardium (the sac that surrounds the heart), the esophagus (swallowing tube), diaphragm (large muscle that brings air in and out of the lungs), and stomach also have receptors that can initiate a cough. If you have GERD, for example, acid from the stomach that creeps up into the esophagus can irritate receptors in the lower esophagus, triggering a cough.
Coughing can be caused by many different conditions and illnesses Table 01. Bronchitis caused by cigarette smoking is the leading cause of chronic cough. Among non-smokers, coughs are usually the result of an upper respiratory infection (such as acute bronchitis, the common cold, or the flu); postnasal drip, asthma, or gastroesophageal reflux disease (GERD). These conditions are by far the most common causes of chronic cough. Among children, sinus infections (sinusitis) are also a common cause. More serious conditions that may cause cough, such as tuberculosis, are not nearly as common.
Table 1. Common Causes of Coughing
Cause Comments Viral infections, such as the common cold, influenza (the flu), croup, and acute bronchitis In non-smokers, viral infections are the most common cause of cough. The excess mucus produced by these infections trigger the cough. Postnasal drip Mucus dripping down the back of the throat can lead to a chronic cough. Many acute respiratory illnesses can cause short bouts of postnasal drip. Chronic postnasal drip is usually the result of a sinus infection (sinusitis) or allergies. Asthma Asthma causes the airways to become clogged with mucus, which then stimulates coughing. In people with mild asthma, coughing is sometimes the only symptom of the disease. Gastroesophageal reflux disease (GERD) When acid from the stomach backs up into the lower esophagus, it can irritate nerve receptors, leading to a persistent dry cough. Less commonly, tiny particles of the acid are aspirated into the lungs, triggering a cough to expel the unwanted substance. Smoking Cigarette smoke contains irritants that the lungs try to get rid of through coughing. In addition, prolonged exposure to smoke destroys cilia, the tiny hairlike formations that line the airways and whose job it is to sweep harmful materials from the lungs. Once cilia are destroyed, mucus cannot be expelled normally, which leads to a chronic cough. Inhalation of a foreign object If a tiny object or piece of food is accidentally inhaled into the lower respiratory tract, it can trigger a violent cough. Stress A cough that disappears during sleep may be caused by stress. Allergies Allergies can lead to postnasal drip, which can trigger a chronic cough. Bacterial infections, such asbronchiectasis, (the abnormal destruction and widening of the large airways), bacterial pneumonia, pertussis (whooping cough) or sinus infection (sinusitis) The excess mucus produced by these infections trigger the cough. With bacterial infections, the mucus coughed up is often rusty or greenish in color. Congestive heart failure A dry, persistent cough is a symptom of congestive heart failure. Often, the cough worsens at night. Environmental pollution Breathing in irritants, such as tobacco and other smoke, dust, and noxious fumes can trigger a cough. Emphysema A chronic, mild cough is a symptom of emphysema. Lung cancer Among non-smokers, a chronic cough is rarely a sign of lung cancer. Coughing can be a symptom of lung cancer among smokers, but most smokers are used to a ?smoker's cough,? and tend not to report it to their doctor. Atelectasis (partial lung collapse) A partial lung collapse can be caused by foreign objects or secretions that block the airways, lung disease, or a tumor pressing on a lung. The body then stimulates the coughing reflex in an attempt to clear the airways. Certain medications Angiotensin-converting enzyme (ACE) inhibitors and beta-blockers, which are both prescribed to treat high blood pressure, can cause a chronic dry cough in some people who take the drugs. Habit Some people cough out of habit or nervousness. Emotional or psychological problems More common in children than adults, a psychogenic cough has no apparent physical cause, but is related instead to an underlying emotional or psychological problem. Tuberculosis One of the symptoms of this disease is a dry cough that eventually may turn into a productive cough with blood-stained sputum.
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