Persistent Cough: Causes and When to Worry

How long should a cough last?

Doctors group coughs by how long they have lasted, because the likely causes differ:

In children, a cough lasting more than 4 weeks is considered chronic.

Lingering cough after a cold

After a respiratory infection, the airway lining stays inflamed and oversensitive for weeks. Even small triggers such as cold air, talking or laughing set off coughing. This post-infectious cough is usually dry, gradually improves and clears within 8 weeks. Antibiotics do not help.

Common causes of a chronic cough

Upper airway cough syndrome (post-nasal drip)

Mucus from the nose and sinuses drips down the throat, causing frequent throat clearing and a cough, often worse lying down. Causes include allergies, chronic rhinitis and sinusitis. See post-nasal drip.

Asthma

Asthma can cause a cough without obvious wheezing (cough-variant asthma). Clues are coughing at night, with exercise, cold air or allergens, and a personal or family history of allergies or eczema. A related condition, non-asthmatic eosinophilic bronchitis, causes a similar cough with normal breathing tests.

Acid reflux

Gastroesophageal reflux can trigger cough through the esophagus or by small amounts reaching the throat. Many people with reflux cough have no heartburn. Coughing after meals, on lying down, with hoarseness or throat clearing suggests it.

Smoking and vaping

Smoker's cough is the most common chronic cough worldwide and often signals early COPD. A change in the usual cough is a warning sign.

ACE inhibitor medicines

Blood pressure medicines whose names end in "-pril" (lisinopril, enalapril, ramipril) cause a dry, tickly cough in about 1 in 10 people. It can start weeks or months after starting the medicine and takes 1 to 4 weeks, sometimes longer, to settle after stopping. Your doctor can switch you to another medicine.

Whooping cough

Whooping cough (pertussis) causes coughing fits that can last 10 weeks or more, sometimes ending in a whoop or vomiting. Adults often have a milder but long-lasting cough. It is dangerous to young babies, so pregnant women are offered a booster vaccine in each pregnancy.

Less common but important causes

• Lung cancer: a new or changing cough in smokers or ex-smokers, blood in sputum, weight loss, breathlessness
• Tuberculosis: cough lasting over 3 weeks with fever, night sweats and weight loss, especially after travel or exposure
• Bronchiectasis: daily cough with large amounts of sputum and repeated chest infections
• Interstitial lung disease: a dry cough with gradually increasing breathlessness and crackles in the lungs
• Heart failure: cough worse lying flat, with breathlessness and swollen ankles
• Inhaled objects: especially in young children, with sudden coughing that started during eating or play
• Chronic cough hypersensitivity: an oversensitive cough reflex that remains after other causes are treated

Dry vs wet persistent cough

• Dry cough: post-viral cough, asthma, reflux, ACE inhibitors, interstitial lung disease, cough hypersensitivity
• Wet or productive cough: smoking and COPD, bronchiectasis, post-nasal drip, chronic bronchitis, sometimes infection

When to see a doctor

See a doctor if your cough lasts more than 3 weeks, or sooner if you have any red flag: coughing blood, weight loss, night sweats, fever, breathlessness, chest pain, hoarseness lasting over 3 weeks, or a change in a long-standing smoker's cough.

How doctors find the cause

The doctor will ask how long you have coughed, whether it is dry or wet, what triggers it, about smoking, medicines, allergies, heartburn, nasal symptoms, travel, exposures at work and contact with tuberculosis or whooping cough. They will listen to your chest and look in your nose and throat.

Common tests:

• Chest X-ray: recommended for most adults with a cough lasting over 8 weeks
• Spirometry, sometimes with a bronchodilator or challenge test, for asthma and COPD
• FeNO test: measures airway inflammation linked to asthma
• Sputum tests for infection or tuberculosis
• CT scan of the chest or sinuses when needed
• Pertussis testing in the first weeks of coughing fits

Often, the most useful "test" is a trial of treatment for the most likely cause, such as an inhaled steroid for asthma or a nasal steroid for post-nasal drip.

Treatment for a persistent cough

Treat the cause

• Stop smoking or vaping, with support and nicotine replacement
• Switch from an ACE inhibitor to another blood pressure medicine
• Steroid nasal sprays and antihistamines for post-nasal drip
• Inhaled steroids and relievers for asthma
• Reflux measures and, if appropriate, acid-reducing medicine
• Antibiotics only for confirmed bacterial infections, including whooping cough and tuberculosis

Soothing measures

• Honey in warm water or tea (not for babies under 12 months)
• Warm drinks and staying hydrated
• Sucking lozenges or hard candies
• Avoiding smoke, strong perfumes and cold dry air

Over-the-counter cough medicines have little proven benefit, and cough and cold medicines should not be given to children under 6 (US guidance advises against them under 4, and many experts under 6). For persistent unexplained cough, specialists may use speech therapy techniques and certain nerve-calming medicines.

Frequently asked questions

Why won't my cough go away?

The commonest reason is a post-viral cough that lingers for weeks after a cold. If it lasts more than 8 weeks, likely causes are post-nasal drip, asthma, acid reflux, smoking or ACE inhibitor medicines. A doctor can check for less common causes such as whooping cough or lung disease.

How long is too long for a cough?

See a doctor if a cough lasts more than 3 weeks, or at any time if you cough up blood, lose weight, have night sweats, fever or breathlessness. A cough lasting more than 8 weeks is chronic and usually needs a chest X-ray.

Is a persistent dry cough serious?

Usually not. Most persistent dry coughs are post-viral, asthma-related, reflux-related or due to ACE inhibitors. Less often they signal lung scarring, heart failure or cancer, especially with breathlessness or weight loss. A doctor's assessment is worthwhile if it lasts beyond 3 weeks.

Can acid reflux cause a persistent cough?

Yes. Reflux is one of the commonest causes of chronic cough, and many people have no heartburn. A cough after meals, when lying down, or with hoarseness and throat clearing suggests reflux. Changes to meal timing, raising the head of the bed and sometimes medicine can help.

Should I get a chest X-ray for a cough?

A chest X-ray is recommended for a cough lasting more than 8 weeks, and sooner for smokers, people over 40 with a new cough, or anyone with red flags such as coughing blood, weight loss or breathlessness.