A cough is the body's method of removing and expelling foreign bodies or mucus from the lungs and airways. 
How a cough occurs
Sensory receptors located in the respiratory tract send a stimulus to the brainstem when sensing the presence of a foreign body or an inflammation. This leads to a reflex that activates the respiratory muscles and the diaphragm in a coordinated manner to rapidly and forcefully move air into the respiratory tract in response to the stimulus sent by the receptors. 
A cough is defined as a cough accompanied by phlegm when there are secretions expelled during coughing. These secretions are generally mucus produced in the airways to protect and clean them from pollutants and small foreign bodies. 
As is known, a productive cough, meaning a cough accompanied by various secretions, may contain different substances, such as: blood, mucus, or pus. The color of these secretions can be green, yellow, white, pink, or dark red. 
Symptoms of a Cough with Phlegm
A cough in itself is a symptom, not a disease. Usually, the true nature of a cough and its causes only become apparent after the appearance of other symptoms, or after conducting accurate physical and imaging examinations. 
Causes and Risk Factors of a Cough with Phlegm
As mentioned, a cough with phlegm is accompanied by the secretion of salivary substances called phlegm or mucus. The source of this saliva is either the lungs, i.e., in the bronchioles located inside or outside the lungs, or from a higher source, such as: the nose or sinuses. In this case, the saliva moves to the airways due to the effect of gravity via the back of the throat. 
The most prominent causes of a cough with phlegm include the following: 
1. Viral Disease
It is very common for a cough with phlegm to accompany viral diseases, such as: the common cold or the flu. In this case, the cough usually occurs due to mucus draining from an upper source via the back of the throat. 
2. Catching an Infection
An infection of the lungs or the respiratory tract connected to the lungs can lead to a cough with phlegm. The diseases we are talking about in such a case include: 
•    Pneumonia. 
•    Bronchitis. 
•    Sinusitis. 
•    Tuberculosis. 
3. Chronic Lung Diseases
A cough with phlegm usually accompanies serious chronic lung diseases, such as: Chronic Obstructive Pulmonary Disease (COPD), where a cough accompanied by phlegm is one of the symptoms of the exacerbation of the disease that has affected the respiratory tract. 
4. Gastroesophageal Reflux Disease (GERD)
Stomach acids refluxing through the upper esophageal sphincter can cause a cough, and this cough often occurs during the night due to gravity. 
5. Mucus Drainage via the Back of the Throat
This is what causes the urge to clear or scratch the throat, and this is one of the common and widespread cases. 
6. Smoking
The damage inflicted on the respiratory tract and lungs by smoking causes a chronic, mucus-filled cough. 
Complications of a Cough with Phlegm
The most common complications of having a cough include: 
•    Pain in the chest and abdomen. 
•    Inability to control urine, and urinary incontinence during coughing. 
•    Fatigue. 
•    Fainting and temporary loss of consciousness, due to decreased venous return of blood to the heart resulting from elevated positive pressure in the chest. 
•    Rib fractures, even in healthy individuals, due to coughing. 
Diagnosis of a Cough with Phlegm
A cough is a pathological symptom in itself and not a disease, and the doctor must conduct a comprehensive physical examination to identify other symptoms that could help us diagnose the causes of the cough. The examinations that could help us diagnose and determine the causes of a cough in such cases are: 
1. Blood Oxygen Saturation Test
This is done using an electrical measuring device placed on one of the fingers. 
2. Lung Function and Maximum Expiratory Capacity Test
Or what is called spirometry, which helps in the diagnostic process for some medical conditions like asthma or various lung diseases. 
3. Imaging Tests
Which can help diagnose and determine the causes of a cough, namely chest X-ray imaging, as this test is conducted when there are indications of disease infection during the physical examination and auscultation of the lungs. A computed tomography (CT) scan of the sinuses in the skull may also be performed to verify their infection. 
4. Throat Swab
To detect pertussis (whooping cough) bacteria. 
5. Other Tests
To detect a cough from an upper source, a post-nasal drip test is performed, as well as a lung function test, and even an esophageal acidity test to detect gastroesophageal reflux. 
Treatment of a Cough with Phlegm
Treatments vary according to the nature of the cough as follows: 
1. Treatment of an Acute Cough
The disease causing the cough, the cough reflex, and various factors that increase the severity of the cough must be treated, through: 
•    Antiviral drugs: To treat viral infections, which are rarely given. 
•    Antibiotics: To treat bacterial infections. 
•    Beta-agonist medication: A patient suffering from bronchitis can be given this medication to alleviate the severity of the cough. 
•    Post-nasal drip treatment: Using antihistamine drugs, steroids, or blood vessel decongestants. 
•    Gastroesophageal reflux treatment: Done with drugs that reduce stomach acid production. 
2. Treatment of the Cough Reflex
This is done by taking drugs that affect the brainstem and raise the minimum threshold required to stimulate a cough, and of course, this is done after consulting a doctor. 
3. Chronic Cough
Treatment is carried out as follows: 
•    Pertussis treatment: Using antibiotics to reduce the infection. 
•    Treatment of a chronic cough with no known source: By inhaling a local anesthetic and Morphine Sulfate. 
Prevention of a Cough with Phlegm
The prevention process for a cough revolves around attempting to prevent its causes, and the most important of these methods are: 
•    Maintaining personal hygiene during the winter to reduce the chances of catching viral and bacterial diseases. 
•    Abstaining from smoking, whether direct or passive smoking. 
•    Protection from environmental pollutants. 
•    Maintaining a healthy diet to strengthen the immune system. 
Alternative Treatments
It should be noted that Echinacea and Vitamin C are not considered effective treatments if used after the appearance of a cough. 
Follow these steps to help treat a cough with home methods: 
Thyme
Thyme helps in treating a cough and infections of the upper respiratory tract and bronchi, as it contains compounds that suppress coughing, and it helps relax throat muscles and reduce inflammation and headaches. To prepare a thyme drink, do the following: 
•    Mix two teaspoons of ground thyme with a cup of hot water. 
•    Cover it for 10 minutes. 
Flax, Honey, and Lemon
Boiling flaxseeds and consuming them will help soothe the bronchi and reduce coughing. You can add honey and lemon due to their anti-inflammatory properties. Perform the following steps: 
•    Boil two to three tablespoons of flaxseeds in a cup of water. 
•    Add three tablespoons of honey and fresh lemon juice. 
Lemon
Lemon has great properties that help you get rid of the annoying cough you suffer from, so put some black pepper and salt on a lemon and eat it. 
Milk
It is considered one of the home remedies that help you treat a cough, so mix some honey with milk before consuming it.