A cough is one of the most common reasons patients seek medical care. Most coughs resolve within a few days or weeks. But when a cough continues for more than eight weeks in an adult, we consider it a chronic cough and begin looking more carefully for an underlying cause — or more commonly, causes. As a Board-Certified specialist in Allergy, Asthma & Immunology, I frequently see patients who have been dealing with a persistent cough for months, or sometimes even years. Many have already tried cough medicines, antibiotics, inhalers, acid-reducing medications, or other treatments without lasting relief. The key to managing a chronic cough is understanding why you are coughing in the first place.
There isn't one test that diagnoses every chronic cough. Instead, the evaluation often involves several pieces of information, including your medical history, physical examination, pulmonary testing, allergy evaluation, and, when appropriate, evaluation of the nose, sinuses, and throat. It is rare for a patient who seeks a specialist's opinion for a chronic cough to have only a single triggering factor.
Here is what you can expect an evaluation to include.
Step 1: A Detailed History
Before ordering tests, I want to understand your cough. Important questions include:
- How long have you been coughing?
- Is the cough dry or productive? Is there mucus, and what color is it?
- Is the cough worse at night?
- Does exercise or cold air trigger it?
- Do you cough when talking or laughing?
- Do you have wheezing or shortness of breath?
- Do you experience nasal congestion or drainage?
- Do you frequently clear your throat?
- Do you have heartburn, reflux, or a sensation of something in your throat?
- Did the cough begin after a respiratory infection such as COVID-19?
- Are you exposed to smoke, vaping, dust, pets, mold, or occupational irritants?
- Do you notice a sore throat after awakening in the morning?
- What medications are you taking? Are you on an ACE inhibitor?
I will also want to know what treatments you've already tried and, importantly, whether they helped at all. This history helps determine which diagnostic tests are most useful.
Step 2: Pulmonary Function Testing (PFT)
One of the most important parts of a chronic cough evaluation is determining whether the lungs and airways are functioning normally. This is where pulmonary function testing (PFT) becomes extremely valuable.
A pulmonary function test measures how well you move air in and out of your lungs. During testing, you'll be asked to breathe into a specialized device called a spirometer. You'll take a deep breath and then blow out as forcefully and completely as possible, then breathe back in again as fast as you can. It may sound simple, but the technique matters — you'll usually perform several attempts so that we can obtain reliable measurements.
PFTs can help identify patterns associated with:
- Asthma
- Airway obstruction
- COPD
- Restrictive lung disease
- Other abnormalities affecting breathing
What if my PFT is normal?
A normal spirometry test does not necessarily rule out asthma. Some patients with intermittent or mild asthma can have normal lung function when they are not actively experiencing airway narrowing. When the clinical history suggests asthma but baseline spirometry is normal, additional testing — typically bronchodilator testing after albuterol — is appropriate. This is one reason I do not diagnose or rule out asthma based on symptoms alone.
Step 3: Allergy Skin Testing
Another important question is whether allergies are contributing to your cough. Allergic inflammation can cause nasal congestion, sneezing, itching, postnasal drainage, and throat irritation. For some patients, the sensation of drainage or irritation in the upper airway can contribute significantly to chronic coughing.
Allergy skin testing involves placing small amounts of an allergen into the superficial layer of the skin with a prick device and observing for a localized reaction. This does not break the skin and no bleeding occurs. Depending on your history, testing may include:
- Dust mites
- Cat and dog allergens
- Grass, tree, and weed pollens
- Molds
A positive test tells us that your immune system is sensitized to that allergen and is making allergic antibody called IgE. However, a positive allergy test does not automatically mean that the allergen is causing your cough. We interpret the testing in the context of your symptoms, exposure history, examination, and other test results.
Step 4: Looking Beyond the Lungs — Your Nose, Sinuses, and Throat
One of the most important concepts in evaluating chronic cough is that the source of the cough may not be the lungs, even though you might believe that is the origin. Patients with chronic rhinitis and chronic sinus infections experience postnasal drainage, nasal obstruction, or inflammation around the throat and voice box. This can cause frequent throat clearing, hoarseness, and persistent coughing. When the symptoms or examination suggest a sinus problem, I may recommend evaluation by an ENT (Ear, Nose and Throat) Specialist.
Step 5: ENT Evaluation and Rhinolaryngoscopy
Your ENT specialist may perform a procedure called rhinolaryngoscopy, often using a small flexible camera. This allows the specialist to directly examine areas that cannot be adequately evaluated simply by looking into the mouth or nose.
The examination may provide information about:
- The nasal passages and the back of the nose
- The throat and larynx (voice box)
- The vocal cords
- Signs of inflammation
- Structural abnormalities
- Other potential sources of chronic irritation
This can be particularly helpful when a patient has symptoms such as chronic throat clearing, hoarseness, a sensation of drainage, nasal obstruction, or a cough that seems to originate primarily from the throat.
Step 6: CT Scan of the Sinuses — When Indicated
Every patient with a chronic cough needs a chest X-ray, and some patients need a sinus CT scan. When symptoms and examination raise concern for significant or chronic sinus disease, a CT scan of the sinuses can provide much more detailed information about the anatomy and the presence of infection.
A sinus CT can help evaluate:
- Chronic sinus inflammation
- Sinus obstruction
- Anatomical abnormalities
- Nasal polyps
The goal is not to order every possible test. The goal is to order the right test for the clinical question we are trying to answer.
Putting the Pieces Together
A chronic cough is often more complicated than simply asking, "Do I have asthma?" In many patients, there may be more than one contributing factor. For example, a patient might have allergic rhinitis causing nasal inflammation and drainage leading to throat irritation and cough — while at the same time having asthma causing airway hyperresponsiveness, cough, and intermittent wheezing. When this occurs, all contributing factors typically need to be treated simultaneously to see improvement.
A Chronic Cough Is a Symptom — Not a Diagnosis
One of the biggest mistakes we can make with a persistent cough is assuming that every patient has the same problem. A cough that occurs after COVID-19 is not necessarily asthma. A cough with throat clearing is not necessarily reflux. A cough with nasal drainage is not necessarily a sinus infection. And a positive allergy test does not necessarily mean allergies are the reason you're coughing. The diagnostic process matters.
When Should You See a Specialist?
Consider an evaluation if your cough:
- Has persisted for more than eight weeks
- Keeps returning
- Interferes with sleep
- Limits exercise or physical activity
- Is associated with wheezing or shortness of breath
- Occurs with chronic nasal congestion or drainage
- Is accompanied by frequent throat clearing or hoarseness
- Has not improved despite previous treatment
A persistent cough deserves more than another bottle of cough medicine. Finding the cause is the first step toward finding the right treatment.
A Note From Your Allergy, Asthma & Immunology Specialist
My approach to chronic cough is to look at the entire respiratory system — from the lungs and airways to the nose, sinuses, throat, and immune system. When appropriate, pulmonary function testing and allergy skin testing can help identify lower- and upper-airway contributors. Collaboration with ENT, including rhinolaryngoscopy and sinus imaging when indicated, can provide another important piece of the puzzle. The goal is simple: don't just suppress the cough. Find out why you're coughing.
This article is intended for general educational purposes and does not replace an individualized medical evaluation. Diagnostic testing should be determined by your healthcare provider based on your symptoms, medical history, examination, and risk factors.