Causes and Risk Factors of Cough

While a cough is one of the most common reasons people see their primary care doctor, the cause of a cough can vary greatly—from the common cold or the flu to allergies, pulmonary disease, or even acid reflux.

In each of these cases, the cough is meant to clear an irritant, obstruction, microorganism, or fluid from the airways. It can be reflexive (automatic) or induced (something you do intentionally).

This article details the many conditions and lifestyle factors that can bring on a cough.

Common Causes

While there will invariably be some overlap in the causes behind acute, sub-acute, and chronic coughs (for example, since chronic illnesses can often have acute flare-ups called exacerbations), how long you've had a cough is often the first clue as to what the underlying cause of it is.

Acute Cough

Broadly speaking, an acute cough is either the sign of a rapidly developing infection or an acute exacerbation of a chronic illness.

The most common causes of an acute cough include:

• Common cold
• Influenza
• Upper respiratory infection (including sinusitis, pharyngitis, and epiglottitis)
• Acute bronchitis
• Croup
• Respiratory Syncytial Virus (RSV)
• Upper airway cough syndrome (a.k.a. post-nasal drip, often related to allergic rhinitis or non-allergic rhinitis)
• Chronic obstructive pulmonary disease (COPD) exacerbations
• Gastroesophageal reflux disease (GERD) exacerbations
• Acute left heart failure with congestion
• Asthma exacerbations
• Covid-related upper respiratory infection and cough

Pertussis, for example, tends to affect babies and has a distinctive, dry cough. By contrast, COPD mainly affects adults and has a "chesty" productive cough with plenty of mucus. The presence of fever, chills, and muscle aches can help differentiate infectious causes from non-infectious ones.

These clues can work together to help diagnose the underlying cause of a cough. A detailed medical history (including smoking history, family history, medication use, and previous respiratory infections) is also vital.

Sub-Acute Cough

A sub-acute cough is a "middle-of-the-road" classification that helps separate the causes of an acute cough from those of a chronic cough. Most often, a sub-acute cough is the aftermath of an upper respiratory infection that has simply lingered on.

For a cough lasting between three and eight weeks, the most common causes are:

• Post-infectious cough (typically viral)
• Bacterial sinusitis
• Asthma (also known as cough variant asthma)

The diagnosis of a subacute cough is similar to that of an acute cough and includes a physical exam and review of your medical history. If asthma is suspected, your healthcare provide will use a peak flow meter. If that is inconclusive or unclear, bronchoprovocation testing (in which an allergist exposes you to a variety of common asthma triggers) may be ordered.

Chronic Cough

A chronic cough is one that lasts for more than eight weeks but can sometimes persist for years. Although a chronic cough can be attributed to any number of conditions, the majority of cases are related to a small handful of them.

The seven most common causes of a chronic caugh are:

• Upper airway cough syndrome (especially in people with compromised immune systems)
• Asthma
• GERD (especially a form known as laryngopharyngeal reflux)
• Chronic bronchitis due to smoking
• pertussis, HIV, inflammatory bowel disease, and autoimmune diseases)
  
• The use of angiotensin-converting-enzyme (ACE) inhibitors (such as lisinopril and similar drugs ending with "-pril")

Less common causes of chronic cough include:

• Sarcoidosis (an inflammatory condition that causes the formation of granular clumps in the lungs and other organs)
• Tuberculosis (TB)
• Bronchiectasis (the widening of the airways caused by numerous conditions, including COPD)
• Non-asthmatic eosinophilic bronchitis (NAEB)
• Heart failure
• Bronchogenic carcinoma (cancer primarily affecting the airways of the lungs)
• Cancer metastasis (spread of cancer) to the lungs
• Pharyngeal dysfunction, in which the passage between the mouth and windpipe malfunctions, allowing food and other substances to enter the lungs
• Psychogenic cough (a habitual cough of psychological origin)

Because the causes of a chronic cough are so diverse, lab testing and imaging studies are usually required. In some cases, the healthcare provider may simply advise you to avoid certain drugs or irritants to see if the cough clears. With ACE inhibitors—drugs most commonly used to control high blood pressure—it can take up to four weeks before a cough fully resolves.

Lifestyle Risk Factors

Any inhaled substance that irritates or obstructs the airways can trigger the cough reflex. Persistent exposure to these substances can lead to a condition known as cough hypersensitivity in which you become abnormally sensitive to inhaled substances. This is related to changes in the brainstem that amplify the nerve signals that induce cough.

While smoking is a common cause—and a lifestyle factor you can readily change⁠—there are other irritants that are just as impactful.

There are certain risk factors that can increase your risk of cough hypersensitivity and, with it, the duration or severity of a cough. They include:

• Smoking (including second-hand smoke)
• Vaping
• Allergies (especially seasonal allergies)
• Air pollution
• Industrial fumes, smoke, dust, and aerosolized chemicals
• Uncontrolled asthma

Avoidance can go a long way toward reducing the incidence, frequency, and, in some cases, severity of a cough.

Smokers often will have an increased cough for a week or so when they stop smoking as the cilia in their respiratory epithelium (lining) start to "wake-up" and become active again producing and clearing mucous.

A Word From Verywell

Everyone coughs from time to time. Even if you do it frequently, the reason behind it may be something as simple as an irritant in the air or allergies. That said, coughing can be a sign of an acute or chronic issue that may require treatment. When in doubt, seek an evaluation from your healthcare provider.