What Is The Cause Of Persistent Dry Cough?

Cough is a common complaint and a frequent cause of seeking medical consultation. It is a reflex of the body to irritants in the airway but can also be a warning sign of several respiratory and non-respiratory diseases.

Acute or short-lived cough usually occurs due to infections of the upper respiratory tract and is self-limiting and resolves within three weeks.

However, chronic cough can persist for more than eight weeks. Chronic cough causes exhaustion and fatigue, interrupts sleep, impairs concentration and work performance. It can also be a considerable source of distress and anxiety as the treatment and diagnosis can stretch over weeks.

However, many chronic cough cases do not have a specific identifiable cause. The most common causes of chronic persistent dry cough include underlying conditions like post nasal drip, gastroesophageal reflux disease (GERD), asthma and smoking. 

What is dry cough?

Cough is a natural defence mechanism of the body. It helps clear out the throat of any irritants or collection of fluid. Dry cough is a cough that does not produce any mucus. It occurs as a result of a tickling sensation in the throat. As no mucus is produced and no sputum (phlegm) is cleared out from the throat by this cough, it is called an unproductive cough.

Causes of dry cough:

Common causes of persistent dry cough:

1. Post nasal drip or the upper airway cough syndrome – when the nasal membranes are irritated by viruses, allergies, sinusitis, dust particles, and airborne chemicals, there is an increase in the production of mucus from the nose. The nose becomes runny and stuffy. This mucus can drip down the back of the nose into the throat, triggering cough. This cough is worse during the night time as lying down can make the person more aware of the dripping feeling in the back of their throat
2. Asthma – Chronic dry cough is a common symptom in people suffering from asthma. In certain cases, cough can even just be the only symptom of asthma in the absence of wheezing and breathlessness. (Cough variant asthma). In this case, the cough occurs at night
3. Gastroesophageal reflux disease (GERD) – GERD is the reflux of acid from the stomach into the food pipe. It has been seen to cause chronic cough in as many as 40% of the cases. Acid irritates the nerves in the food pipe triggering cough¹
4. Use of ACE inhibitors – ACE inhibitors are a group of medicines used to treat high blood pressure. They can cause dry cough in some people. Some examples of ACE inhibitors are enalapril and lisinopril
5. Infections – a dry cough can linger on in the recovery period of infections like pneumonia, flu, and other types of lung and upper respiratory tract infections. Whooping cough is an infection of the respiratory tract caused by a bacteria, Bordetella Pertussis, in which chronic cough can last for weeks
6. Cough hypersensitivity syndrome – is a condition in which cough reflex is very sensitive and produces a troublesome cough on stimulation by triggers in the environment^2,3

Causes in smokers:

1. Cigarette smoke itself – chemicals in the smoke causes irritation and inflammation of the airways. This condition is commonly known as smoker’s cough
2. Lung infections – smoking can increase the risk of developing lung infections
3. Lung cancer – is a serious cause of persistent dry cough in smokers

Less common causes

1. Airborne environmental irritants – continuous exposure to irritants in the environment can cause chronic cough and even lead to the development of lung conditions termed occupational lung diseases. Air that is too cold or too dry can also cause cough
2. Aspiration during swallowing – abnormal swallowing can cause food particles to enter the airways instead of the food pipe. This can trigger cough reflex
3. Psychological disorders – mental stress can produce various symptoms including cough. This type of cough is worse during periods of stress and absent during sleep
4. Laryngopharyngeal reflux – stomach acid enters up into the throat causing cough
5. Nonasthmatic eosinophilic bronchitis – it is a type of airway inflammation which is not caused by asthma
6. Vocal cord dysfunction –  Patients with vocal cord dysfunction commonly experience noisy breathing and changes in voice because of episodic, uncontrollable narrowing of the cords during inspiration (breathing in). These patients also occasionally experience shortness of breath and cough
7. Obstructive sleep apnoea – this is a condition in which there is abnormal closing or narrowing of the airway during sleep. It has also been recognized as a cause of cough 
8. Sarcoidosis – it is an autoimmune condition in which there is collection of inflammatory cells in different parts of the body, most commonly the lungs
9. Idiopathic pulmonary fibrosis – it is a condition in which there is chronic scarring of the lungs due to an unknown cause
10. Tuberculosis – tuberculosis is an infection of the lungs caused by mycobacterium tuberculosis. It most commonly affects the lung and causes persistent cough

Symptoms of dry cough:

Dry cough is a symptom on its own that could be due to multiple underlying conditions. Symptoms associated with dry cough can help diagnose the underlying conditions.

Symptoms that can accompany a dry cough are:

1. Fever
2. Stuffy or runny nose
3. A feeling of liquid running down the back of the throat
4. Hoarseness and sore throat
5. Shortness of breath and wheezing
6. Sour taste in mouth and heartburn
7. Coughing up blood, a rare and alarming symptom

What is the difference between a dry and wet cough?

Cough is a reflex action of the airway. It can help clear the airways of mucus or fluids and irritants such as dust or smoke to help breathe better.

A cough that is triggered due to the buildup of fluid or mucus in the airways (breathing tubes) is known as a “wet cough” or “Chesty cough”. Doctors also call it a productive cough, as it clears the airways and brings up mucus, also called phlegm or sputum that the person can spit out. This phlegm can be clear, yellow or even green, and is mostly caused by infections of the respiratory system by microorganisms such as bacteria and viruses. People suffering from wet cough feel like there is something stuck in their chest or at the back of their throat (congestion). A wet cough produces a wheezing or rattling sound.

Dry cough does not produce any phlegm or sputum and there is no build of fluids and mucus in the chest or back of the throat. Doctors call it a non productive cough. People with dry cough instead feel irritation like a tickle or scratchy sensation at the back of their throats which makes them cough. 

What to avoid when having a dry cough?

As the underlying cause of a dry cough is irritation and inflammation of the airways avoiding the following can help:

Avoid smoking and secondhand smoke - smoke from cigarettes irritate the airways and the noxious chemicals in the smoke cause inflammation. This can also lead to serious complications like infections, chronic bronchitis, emphysema and lung cancer.

Avoid foods that trigger acid reflux (GERD) – backflow of stomach acid causes irritation and inflammation. Spicy food, heavy fatty food, caffeine, chocolates and acidic foods like tomatoes can all trigger and worsen acid reflux. Avoiding these as well as avoiding having meals 2-3 hours before going to bed is recommended.

Avoid honey in children less than 12 months of age – honey is a great remedy for dry cough and it helps soothe the throat, but it should not be given to children less than 12 months of age as they are at risk of developing a type of food poisoning called infant botulism.

Avoid irritants and allergens such as chemicals, moulds and fragrances

Treatment and remedies:

Establishing the cause of the persistent dry cough is crucial to effective treatment. In some cases, there might be more than one cause that needs to be addressed. 

Quitting smoking:

If you are a smoker, your GP will have a discussion with you regarding your readiness to cut down or quit smoking. They will also provide you with information and support to help you stop smoking. The NHS also provides multiple stop smoking services to help quit smoking.

Changing medications:

If you are taking ACE inhibitors for your high blood pressure and it is causing a nagging cough, your GP will change your blood pressure medication to another suitable medication.

Treatment of allergies and post nasal drip:

Drugs like antihistamines, corticosteroids and decongestants are standard drugs used to treat allergies and post nasal drip.

Treatment of asthma:

Asthma-related cough can be alleviated by treating asthma with inhaled bronchodilators, antileukotrienes, and/or low-dose theophylline. Patients with severe and refractory asthmatic cough are given a trial of oral corticosteroids. These medications help reduce inflammation and open up the airways.

Additionally, non-asthmatic eosinophilic bronchitis has a good response to inhaled corticosteroids.

Treatment of gastroesophageal reflux disease (Gerd):

If the cause of the cough is stomach acid reflux, your doctor will initially advise you on some lifestyle modifications, like avoiding certain foods mentioned above and losing weight if obese, to help improve the symptoms. 

Moreover, medications to help control acid reflux like prokinetics and proton pump inhibitors can be given by your healthcare provider to help alleviate symptoms when lifestyle modifications do not work.

Treatment of infections:

Viral infections like cold and flu tend to cause a dry cough that can linger on in the recovery period. This cough is mostly treated using home remedies and cough suppressants. If the cause of your persistent cough is due to bacterial, fungal or mycobacterial infection (TB), your doctor will provide you with medications such as antibiotics and antifungals to treat it.

Cough suppressants:

Over-the-counter cough suppressants are intended to treat the symptoms but not the underlying disease. They blunt the cough reflex, lessening the cough and providing temporary relief.

However, they should be avoided in cases of wet cough as suppressing it inhibits the natural response of the body to cough out excessive sputum which could potentially be harmful.

Researches also suggest that these over-the-counter cough suppressants, flu medications, syrups, sprays, and tablets do not work any better than inactive medicine (placebo).^[4]

They should be avoided in children below 12 years of age due to the increased risk of overdose and side effects. Both the Food and Drug Administration (FDA) and Medicine and Healthcare Products Regulatory Agency (MHRA) recommend against the use of cold and cough medicines in infants and young children.^4,5

Home remedies

Some basic home remedies to help soothe dry cough are:

1. Drink plenty of fluids and stray hydrated – warm liquids like broth and tea can help soothe the throat
2. Honey and lemon tea - warm honey and lemon tea help soothe the throat. A spoonful of honey is just as effective (or more effective) than cough drops. Honey should not be given to infants below 12 months of age due to the risk of botulism
3. Cough drops and lozenges – sucking on cough drops or lozenges increases the production of saliva and soothes the throat
4. Using humidifiers to moisturize the air – dry air can irritate the airway and cause cough

Do antibiotics help?

Antibiotics are not useful in the majority of cases of dry cough.

Cold and flu tend to cause wet cough. Later dry cough can linger in the recovery period as the airways are irritated and inflamed but the infection at this point has resolved. Cold and flu are mostly caused by viruses. Antibiotics are only helpful in cases of bacterial infections.

Tuberculosis infection of the lungs causes a dry irritating and persistent cough initially. When diagnosed, TB is treated using multi-drug therapy, a combination of different antibiotics called Antituberculous therapy or ATT.

Other causes of dry cough like irritation due to smoking and dust, irritation of airways due to acid reflux and asthma are not infections and hence antibiotics are not helpful. 

When to seek medical attention

Dry cough can become very distressing and affect the quality of life and even sleep when it is persistent and chronic (lasting for more than 4 weeks). Even though chronic cough is usually not serious, it can be a cause of concern especially in smokers or people exposed to cigarette smoke in their environments. Prompt medical attention is required in cases of the following accompanying symptoms with dry cough:

1. Fever, low grade during the evenings
2. High grade fever accompanied with rigors and chills
3. Blood in cough 
4. Unintentional Weight loss
5. Decreased appetite
6. Drenching sweats at night time
7. Lumps and bumps anywhere in the body
8. Swollen neck glands
9. Extreme fatigue and weakness
10. Chest pain, unrelated to the coughing
11. Shortness of breath
12. Wheezing

Summary

A chronic persistent cough can be very distressing both physically and psychologically. Persistent dry cough has been commonly considered to be caused by conditions like gastroesophageal reflux (acid reflux) disease, postnasal drip or asthma and specific treatments for these conditions can help alleviate the cough. In addition, heart failure, allergies, irritants in the environment, sleep apnea and infection with tuberculosis make up the less frequent causes of a nagging dry cough. Certain medications such as those used to treat hypertension can also cause dry cough.

People who smoke or are exposed to cigarette smoke in the environment develop a persistent dry cough called “smoker’s cough” from the harmful chemicals in the smoke. These chemicals can further cause the development of serious complications like emphysema, chronic bronchitis, pneumonia and lung cancer. A lingering cough is a cause of concern in smokers and requires medical attention. Furthermore, if you are experiencing blood in your cough or if your cough is accompanied by fever, unintentional weight loss, night sweats, breathlessness, undue fatigue, or chest pain, you should consult your GP without delay.