A dry cough is a cough where no mucus or very little mucus is expectorated (coughed up). This is known as a non-productive cough. Most conditions that may cause a cough will present as a dry cough in the early stages. As the disease progresses, the productive nature of the cough will become evident.
Coughing is a result of airway irritation which triggers the cough reflex. Apart from expelling irritants from the airway, coughing also removes mucus which may accumulate as a result of hypersecretion from the lining of the airways. Irritation of the airway without excessive mucus production results in a dry cough.This does not mean that no mucus is present in the lung or airways in a dry cough but rather that the quantity of mucus is very little and may not be expectorated upon coughing.
Cause of a Dry Cough
As mentioned, most coughs may initially start off as a non-productive cough (dry cough) but can progress to a productive cough (wet cough) with time. Apart from certain infections, any irritation of the airway as result of allergies, air pollution, cigarette smoking and certain drugs may result in a dry cough.
Most upper respiratory tract infections may present with a dry cough as the mucus hypersecretion tends to affect the nasal passages and surrounding areas like the paranasal siuses. However, if the infection progresses lower down the respiratory tract or if the mucus drains into the lower airways, a productive cough may be noticed.
A lingering cough following a respiratory tract infection is one of the more common causes of a dry cough. This is a result of bronchial hyper-reactivity and is more prominent in asthmatics (reactive airway disease).
Of the various infections, laryngitis and tracheitis is more likely to present with a dry cough compared to the lower parts of the respiratory tract (bronchi and bronchioles) or lungs. While infectious pneumonia is most likely to present with a wet cough, interstitial pneumonia may result in a dry cough.
Croup (usually viral) and whooping cough (bacterial) are two other infectious causes of a dry cough although less frequently it may present as a productive cough as well, esecially if there is a secondary infection.
Necrotic tonsillitis, often as a result of GERD or chronic infections may also result in a chronic dry cough and patients typically report coughing up food particles that gets trapped within the ulcers and crevasses.
Common causes of a non-infectious dry cough includes asthma, GERD and post nasal drip.
Asthma usually presents with a dry cough, which is easily triggered by any allergen or irritant in the air due to a hyper-reactive airway. White to yellow mucus may at times be expectorated in asthmatics.
In GERD (gastroesophageal reflux) the rising gastric acid, especially after large meals and when sleeping, may irritate the throat (reflux pharyngitis) and trigger a dry cough. Aspiration in GERD however, may cause significant inflammation in the respiratory tract and could result in mucus production (wet cough).
Post-nasal drip is another common cause of a dry cough both in children and adults. However, excessive mucus draining into the respiratory tract and restrained coughing may result in a productive cough as mucus accumulates in the lower respiratory tract. In infectious causes like sinusitis, the lower respiratory tract may also get infected.
Environmental, Occupational and Lifestyle
Cold, dry conditions may cause dryness and irritation of the airways. This will often result in an acute dry cough. The cough usually resolves as a person becomes acclimatized to these conditions.
Air pollution is another common cause of a persistent dry cough and is usually associated with smog and industrial pollution. A greater chance of respiratory infections may exist in chronic exposure to pollutants and this will result in bouts of productive coughing. Chronic obstructive pulmonary disease (COPD), particularly chronic bronchitis, may occur over time and result in a persistent wet cough.
Long term cigarette smokers and those exposed to secondary cigarette smoke may also develop a chronic dry cough for the same reasons as those exposed to air pollution.
Occupational lung diseases is commonly caused by exposure to organic and non-organic dusts (like asbestos, silica, textile fibers), noxious gases (like chlorine, ammonia) and radiation.
Interstitial Lung Disease
In interstitial lung disease, a number of causes may result in severe scarring of the lung tissue. This permanently impairs pulmonary function and a dry cough is a prominent clinical feature.
It may be caused by :
- Infections like pneumonia
- Occupational exposure to dusts, gases and radiation
- Air pollution
- Autoimmune diseases
- Cancer treatment – radiation treatment and chemotherapy
Lung cancer may present with a persistent dry cough initially but as the condition progresses a productive cough and hemoptysis (coughing up blood) may become evident. Tumors of the pharynx (throat cancer) and larynx (voice box/vocal cord cancer) may also cause a dry irritating cough.
A dry cough is a commonly reported side effect with the chronic use of ACE inhibitors, a drug used in the treatment of hypertension (high blood pressure). Other drugs that may cause a cough includes certain antibiotics, anti-arrhythmia drugs, chemotherapeutic agents, certain medication for psychiatric disorders. The chronic use of some of these drugs may cause interstitial lung disease and thereby lead to a persistent dry cough.