A dry cough is one that produces no mucus or phlegm. It can be triggered by dozens of things, from a simple cold to air pollution to a blood pressure medication you started months ago. The cause usually depends on how long you’ve had it: coughs lasting under three weeks are typically from infections, those between three and eight weeks often linger after a virus clears, and anything beyond eight weeks points to a chronic underlying cause.
How a Dry Cough Works
Coughing is a reflex. You take a deep breath, your vocal cords snap shut, your chest muscles contract to build pressure, and then your airway opens suddenly to blast air outward at high speed. When something irritates the nerve endings in your throat, windpipe, or lungs, this reflex fires whether or not there’s mucus to clear. That’s what makes a dry cough so frustrating: your body keeps trying to expel something that isn’t there, or is too small to cough up.
Viral Infections
The most common reason for a sudden dry cough is a respiratory virus. Coronaviruses (including those behind the common cold and COVID-19), adenoviruses, parainfluenza, and RSV all irritate the airways enough to trigger coughing that may produce little to no mucus. Most of the time the infection itself clears within a week or two, but the cough can stick around much longer.
Post-viral cough, sometimes called a postinfectious cough, typically lasts three to eight weeks after you feel otherwise recovered. The virus is gone, but it leaves behind inflamed, hypersensitive airways that react to cold air, talking, or even laughing. This usually resolves on its own within several weeks without treatment. COVID-19 deserves special mention here: some people develop a lingering cough that persists well beyond the typical postinfectious window, particularly if it’s accompanied by chest tightness or worsens at night.
Asthma and Cough-Variant Asthma
Not all asthma involves wheezing or shortness of breath. In cough-variant asthma, the only symptom is a chronic dry cough lasting more than eight weeks. Lung function tests come back normal, chest X-rays look clear, and there’s no audible wheeze on exam. The giveaway is that the airways are overly reactive to triggers like cold air, exercise, or allergens, and the cough responds to inhaled bronchodilators (the same medications used for typical asthma).
If you’ve had a nagging dry cough for months and no obvious explanation, cough-variant asthma is one of the first things worth investigating, especially if you have a history of allergies or eczema.
Upper Airway Cough Syndrome
This condition, formerly called postnasal drip syndrome, is one of the top three causes of chronic dry cough. It happens when problems in the nose or sinuses, such as allergies, sinus infections, or chronic rhinitis, irritate cough receptors in the upper airway. The mechanism isn’t as simple as mucus dripping down the back of your throat: researchers now believe the cough can also result from direct inflammation of nerve endings in the upper airway, even without a noticeable increase in nasal discharge.
That means you can have upper airway cough syndrome without feeling congested or “drippy.” A persistent throat-clearing sensation or a cough that worsens when you lie down are common clues.
Acid Reflux (GERD)
Stomach acid doesn’t have to reach your throat for you to develop a cough. When acid rises into the lower esophagus, it can stimulate cough receptors directly or trigger a nerve reflex (the vagus nerve) that causes mucus secretion and coughing deeper in the airways. This is called gastroesophageal reflux-related cough, and it’s one of the sneakier causes because roughly 70% of people with it have no typical reflux symptoms like heartburn or a sour taste in the mouth.
If you have an unexplained chronic dry cough and no heartburn, reflux is still on the list. It often worsens after meals, when lying flat, or with certain foods.
Blood Pressure Medications
ACE inhibitors, a widely prescribed class of blood pressure drugs, cause a dry cough in roughly 1.5% to 11% of people who take them. The cough can appear within the first week of starting the medication or develop as late as six months in. It’s persistent, tickly, and often worse at night. The good news: it resolves within a few weeks of stopping the medication and will reliably come back if you restart it. If you’re on a blood pressure pill and developed a new dry cough, check whether it’s an ACE inhibitor.
Air Pollution and Environmental Irritants
Breathing in particulate matter, cigarette smoke, traffic exhaust, sulfur dioxide, or chemical fumes can sensitize the nerve channels in your airways that trigger coughing. Fine particles smaller than 2.5 micrometers (PM2.5) are particularly effective at this because they penetrate deep into the lungs. In one study, a modest increase in PM10 exposure (about 10 micrograms per cubic meter over a 30-day average) raised the prevalence of cough by nearly 5% in adolescents.
The effect starts early in life. Research from a German birth cohort study found that air pollution exposure during a child’s first year was associated with dry cough without infection at ages one and two. A U.S. cohort study found a dose-response relationship between traffic exhaust exposure and recurrent dry nighttime cough in early childhood.
Indoors, common triggers include perfumes, cleaning products, and dry or cold air. People with chronic cough often develop a hypersensitive cough reflex, meaning their airways react to stimuli that wouldn’t bother most people: a whiff of cologne, a change in temperature, or even a long conversation.
Less Common but Worth Knowing
A few other causes round out the picture:
- Eosinophilic bronchitis is an allergic-type inflammation of the airways that causes a chronic dry cough without the airway narrowing seen in asthma. It’s diagnosed by finding elevated levels of certain white blood cells in a sputum sample.
- Acute bronchitis starts as a dry cough that may later produce some mucus, typically following an upper respiratory infection. It usually clears within three weeks.
- Smoking irritates the airways chronically, and while a “smoker’s cough” is often productive, it can be dry, especially early on or after quitting when the airways are still healing.
How Timing Helps Identify the Cause
The single most useful clue is duration. A dry cough under three weeks old is almost always from an acute infection or a new irritant exposure. Between three and eight weeks, a postinfectious cough is the most likely explanation, especially if you recently had a cold, flu, or COVID. Beyond eight weeks, the top three culprits are asthma (or cough-variant asthma), upper airway cough syndrome, and acid reflux. Together, these account for the majority of chronic dry cough cases. Medication-related cough and environmental exposures fill in most of the remaining gap.
Paying attention to when the cough worsens can also help. Worse at night may point to reflux or asthma. Worse after eating suggests reflux. Worse with exercise or cold air leans toward asthma. Worse in certain rooms or buildings suggests environmental irritants. These patterns won’t give you a diagnosis on their own, but they’re exactly the kind of detail that helps narrow things down quickly.