All about Coughs, A Common Respiratory Symptom


Q1. What is a Cough? Why Do We Cough?
As a defensive reflex, coughing occurs when an object enters the airway can causes a tinkling sensation. It sends a signal to the brain, which tells the respiratory muscles to contract and the vocal cords to close. The sudden increase in pressure pushes out the mucus as phlegm. 
An effective cough involves the normal functioning of airway, contraction of respiratory muscles and closure of vocal cords. The phlegm cannot be cleared by coughing if the vocal cords fail to close completely. Some patients are prone to swallowing down food the wrong way, making the airway less responsive to foreign objects. As a result, the patients may cough less, but are more susceptible to aspiration pneumonia.
Q2. What are the differences between a dry cough and a cough with phlegm?
Some people say they have dry cough, or cough without phlegm.  So what do they mean by “dry cough”? How do we know if there is phlegm while coughing?  Actually you can feel the phlegm when it reaches the throat, and see the colour when you spit it out. So why do they cough if there is no phlegm? Usually we don’t say “dry cough”, as the difference lies in the amount of mucus produced.  A small amount of mucus can cause a tickling sensation in the airway. When we cough, the mucus is pushed to the throat, then swallowed via the esophagus, and finally removed from the body through the digestive tract without reaching the oral cavity. That’s why one feels the cough is dry or without phlegm.  But can a cough be dry at all? Occasionally, yes. Some patients may have dry cough when there is a growth in the airway, and the irritation may make them feel like coughing it out, but to no avail. That’s why they may cough frequently without phlegm, while most people cough due to phlegm.
Q3. What does the phlegm colour mean?
What does the phlegm colour mean? Most people think that phlegm is white in colour when bacteria-free, and they may need to take antibiotics when it contains bacteria and appears yellow or green. It is not the case, as the colour only has to do with the amount of white blood cells in phlegm.  What most people think about phlegm colour is not all wrong: in case of phlegm caused by bacteria in the airway or lungs, the immune system sends white blood cells there to fight the bacteria. The resulting phlegm is thick with a large amount of dead white blood cells and thus appears in colour, which varies with the amount white blood cells.
Why does yellow/green phlegm not necessarily indicate the presence of bacteria? For example, in case of airway inflammation in asthma patients, the phlegm appears yellow or green due to a large amount of white blood cells. The colour has nothing to do with bacteria.  
Q4. I cannot cough out the phlegm. Can I swallow it?
Some people never spit. Others may do and choose not to swallow it for hygiene reasons. Is there any difference between swallowing and spitting?
What is phlegm? Phlegm is a type of mucus produced continuously to clear the airway. It traps the dust and germ we inhale. The airway is lined with hair-like projections called cilia, which pushes the phlegm to the throat at 16 strokes per second before swallowing. Normally, the system works around the clock to keep the airway clear and help prevent pneumonia. Thus it is OK to spit even if you don’t know how to spit. As some of you may feel uneasy about spitting in public places, is it harmful to swallow phlegm? There is no need to worry at all. The gastric acid will kill the bacteria when the phlegm enters the stomach. As long as it leaves the airway, there is no difference between swallowing phlegm and spitting it out.
Q5. Is coughing up blood a symptom of lung cancer?
Rather than worry about chronic cough, most people may get frightened easily by coughing blood. Does it mean lung cancer? 
The mucous membrane in the airway is very fragile. A few forceful coughs are more than enough to damage the membrane and cause blood-tinged phlegm. Bloody phlegm does not necessarily suggest lung cancer, and is mostly caused by injury due to severe coughing. Also important is the time when it happens. People with allergic rhinitis may have bloody phlegm when they wake up, possibly due to the blood entering the airway from the nose.  Another common cause of bloody phlegm is bronchiectasis, with symptoms such as frequent coughs and much phlegm, sometimes blood-tinged. Does lung cancer cause bloody phlegm? It is possible. Lung cancer may cause bloody phlegm by causing irritation to the airway or affecting the blood vessels. The causes of blood phlegm are myriad, and for most of the time have nothing to do with lung cancer. Therefore it is important to identify the underlying causes when it occurs.
Q6. In terms of causes, what are the differences between daytime coughing and nighttime coughing/coughing during sleep?
The time of coughing is of great value to diagnosis. We cough whenever there is phlegm in the airway. The phlegm mostly comes from 3 sources: the nose in case of postnasal drip, the stomach during gastroesophageal reflux, and the airway and lungs. Coughing tends to be more severe in the morning and the evening when the symptoms of allergic rhinitis get worse. In case of gastroesophageal reflux, people cough more frequently either when hungry or full.
How about coughing caused by the airway and lung condition as far as time is concerned? The airway usually becomes narrowest during sleep, and coughing is most severe at midnight if it is caused by asthma or chronic tracheitis. Patients with bronchiectasis often cough with phlegm when they wake up in the morning, and it tends to get worse in the evening, in the afternoon or at dusk. They do not wake up coughing when deep in sleep.  Those who do so at midnight may suffer gastroesophageal reflux while lying down. Doctors can determine the causes of coughing based on when it occurs.

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