Elegant may not be the first word that comes to mind when you think of a cough. From a biological perspective, however, the cough reflex is one of your body's most elegant defenses. Through a complex, coordinated series of actions involving your muscles, nerves and respiratory system, a cough clears your airways of accumulated mucus, dust and germs. Although an occasional cough serves you well, a persistent cough typically indicates an underlying medical problem. Asthma and smoking are among the most common causes of coughs. The nature of the cough, related symptoms and your personal history help distinguish an asthmatic cough from a smoker's cough.
Background
Understanding the underlying airway problems associated with asthma and smoking can help you appreciate the different features of coughs that typically occur with these conditions. With asthma, your airways exhibit increased sensitivity. A trigger, such as stress, exercise or an inhaled irritant, causes a sudden episode of airway constriction, reduced airflow and coughing. Between asthmatic episodes, the airways typically relax and airflow returns to normal or near-normal levels. Intense coughing subsides as the attack resolves, but episodic coughing may occur due to ongoing airway hypersensitivity.
A smoker's cough is caused by chronic bronchitis, a condition in which ongoing inflammation provoked by exposure to tobacco smoke or another irritant leads to irreversible airway damage and airflow obstruction. The inflamed airways produce abnormally large amounts of mucus, causing a persistent daily cough.
Smoking History and Age
Your smoking history is an important factor in distinguishing an asthmatic cough from a smoker's cough. Because chronic bronchitis develops over many years, a long-term history of smoking increases the likelihood of this disease. Your age is also a consideration because chronic bronchitis rarely develops before age 40 and most commonly occurs after 50. If you are younger than 40, chronic bronchitis is unlikely to be the cause of a chronic cough.
Wet or Dry
Whether your cough is wet or dry is an important characteristic to consider when trying to distinguish between a smoker's cough and asthma. A smoker's cough is wet; that is, the cough yields mucus from your lungs. The mucus may be yellowish or clear and often contains brown flecks, especially if you are an active smoker. A cough associated with asthma is usually dry, although the coughing associated with an attack often yields thick mucus.
Timing
Paying attention to when you cough can help determine the underlying cause. With asthma, intense coughing typically occurs with attacks. A dry nighttime or early morning cough may also occur. With a smoker's cough, coughing is typically most intense in the morning as you clear the mucus that has accumulated in your lungs overnight. Coughing continues throughout the day but is characteristically less frequent as the day wears on.
Related Signs and Symptoms
A cough associated with asthma is commonly accompanied by wheezing, chest tightness and shortness of breath. Comfortable breathing resumes between asthma attacks. In contrast, chronic bronchitis typically causes persistent shortness of breath due to permanent airway damage and airflow obstruction. Shortness of breath most commonly occurs with physical exertion early in the course of chronic bronchitis. With advanced disease, shortness of breath frequently occurs at rest.
Importance of Diagnosis
Although a smoker's cough and an asthmatic cough share the common underlying features of airway inflammation and airflow obstruction, the two conditions are distinct and managed differently. Additionally, other medical conditions may cause coughing similar to that which occurs with chronic bronchitis or asthma. Because an accurate diagnosis is essential for determining proper medical treatment, see your doctor if you have a persistent cough.
References
- National Heart Lung and Blood Institute; What Is Cough?; October 2010
- American Academy of Allergy, Asthma & Immunology: Asthma
- "Pulmonary Pathophysiology: The Essentials"; John Burnard West, M.D., Ph.D.; 2008
- "Chronic Obstructive Pulmonary Disease in Primary Care"; David Bellamy, B.Sc., M.B.B.S., F.R.C.P., Rachel Booker, R.G.N.; 2004
- Allergy and Asthma Foundation of America; Adult Onset of Asthma; 2005
- "Harrison’s Principles of Internal Medicine, 16th Edition"; Dennis L. Kasper, M.D. et al, editors; 2004
- National Heart Lung and Blood Institute; What Are the Signs and Symptoms of Asthma?; February 2011
- "European Respiratory Journal"; Similarities and Differences Between Asthma and Chronic Obstructive Pulmonary Disease: Treatment and Early Outcomes; A.Sonia Buist, M.D., Ph.D.; January 2003
