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Rising respiratory illness cases -

Countries around the world are experiencing a surge in respiratory illnesses, with flu, RSV, and COVID leading to more severe cases and emergency room visits. Persistent post-viral symptoms (including prolonged coughing) are becoming increasingly widespread among patients.

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Why coughing matters -

Coughing is a protective reflex designed to clear the airway of harmful substances like fumes, food particles, or irritants. This essential function is triggered by nerves in the throat equipped with receptor proteins that react to environmental stimuli like cold air or capsaicin, the chemical that gives peppers their spiciness.

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The brain’s role -

Coughing involves a neural pathway where airway nerves send signals to the brain. The brain then decides whether to initiate a cough, which gives people partial conscious control over some types of coughing in various situations.

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Mysterious post-viral cough triggers -

Scientists are aware of coughing’s purpose and how it can be triggered by different stimuli, but they are still uncertain about what precisely triggers coughs during and after viral infections, especially when dry, non-productive coughs persist after the illness has resolved.

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Terminology -

If a cough remains for longer than eight weeks, then it’s usually considered a chronic cough. If it lasts for three to eight weeks following a respiratory illness, then it is known as a sub-acute cough.

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Wet vs. dry -

Coughing has often been thought of as the body’s way to clear mucus, but viruses might also exploit the reflex to help themselves spread. Yet many infections cause dry coughs that don’t produce phlegm, which leaves unanswered questions about what specific triggers in our nerves initiate this response during illness.

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Inflammation and nerve sensitivity -

Infections cause airway nerves to become hypersensitive due to inflammation. This heightened sensitivity may explain why post-viral coughs occur, as the body’s nerves continue to overreact to normal stimuli long after the infection ends.

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Everyday triggers -

Hypersensitive airway nerves make non-harmful activities like laughing, talking, or exposure to cold air capable of triggering severe coughing bouts. These episodes can persist despite no active infection being present in the body.

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Guinea pig studies -

Research from as early as the 1990s revealed that guinea pigs infected with flu-like viruses showed increased coughing when exposed to irritants. These findings provided early evidence linking viral infections to nerve hypersensitivity.

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The TRPV1 receptor -

More recently, scientists discovered that respiratory virus infections caused certain nerves in the airway to create more copies of the TRPV1 receptor protein in the throat, which reacts to irritants like capsaicin.

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Viral exposure amplifies receptor activity -

Studies on human cells revealed that exposure to viruses, even ones 'killed' by UV light, increased copies of TRPV1 and similar receptors. This supports the idea that exposure to a virus basically means that nerves are primed to become more sensitive.

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A tough-to-shake reflex -

Coughing is a powerful and sometimes painful reflex. Persistent coughing after illness can be so intense that it leads to complications like broken ribs, especially in younger individuals without underlying health issues.

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When to consult a doctor -

If a cough lasts more than eight weeks (or if it’s accompanied by symptoms like fever, shortness of breath, or bloody phlegm), it’s essential to consult a doctor promptly to rule out other potential health issues.

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Early intervention recommended -

While an eight-week threshold defines chronic cough, prolonged episodes of coughing lasting more than one month can still be debilitating. Seeking medical advice earlier can help mitigate discomfort and identify any underlying causes.

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Postnasal drip -

A potential underlying cause of a prolonged cough is postnasal drip, also known as upper airway cough syndrome. This occurs when mucus from membranes in the nose drips into the throat due to allergies, viruses, or irritants. Treatments include decongestants, antihistamines, or nasal sprays tailored to individual symptoms.

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Asthma -

Asthma-related coughing results from airway tightening, swelling, and mucus production triggered by allergens, infections, smoke, exercise, or emotions. Standard treatments include inhaling certain aerosol medications to reduce inflammation and open airways.

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Gastroesophageal reflux disease (GERD) -

GERD-induced coughs arise from stomach acid irritating the esophagus and lungs. Management involves lifestyle changes such as avoiding reflux-triggering foods, weight loss, and proton pump inhibitors. Persistent cases may require further evaluation or advanced treatments.

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Blood pressure medications -

Angiotensin-converting enzyme (ACE) inhibitors used for high blood pressure can cause chronic dry coughing in up to 20% of users. Switching to an alternative medication can effectively resolve this side effect, often without further complications.

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Smoking -

Smoking damages lungs and causes a "smoker’s cough,” which is often an early sign of chronic obstructive pulmonary disease (COPD). Quitting smoking is critical, but lung repair is gradual and may not fully reverse the damage caused by prolonged tobacco use.

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COPD -

COPD, including emphysema and chronic bronchitis, leads to excess mucus and coughing, alongside other symptoms like shortness of breath and airflow obstruction. Treatments include inhalers, steroids, oxygen therapy, and symptom management to slow the progression of the disease.

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Lung cancer -

Lung cancer may present with coughing, and it's often linked to smoking. While non-smokers are less likely to develop this, any persistent cough warrants evaluation. Treatments include surgery, chemotherapy, radiation, or targeted therapies depending on cancer type and stage.

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Refractory cough -

When a cough’s cause cannot be determined and persists despite treatment, it is called a refractory cough. Doctors may prescribe cough-suppressing medications (both prescription and over-the-counter) with caution against prolonged use.

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Initial evaluation -

When doctors diagnose the cause of a person’s cough, they initially conduct a physical evaluation wherein they assess vital signs and listen to the lungs and heart with a stethoscope. A trial treatment may be suggested based on symptoms; if the cough improves, additional testing is typically unnecessary.

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Further testing for persistent coughs -

If the cough continues or the diagnosis remains unclear, further tests may be needed to pinpoint the cause. These tests help identify infections, lung conditions, or other underlying factors contributing to the cough.

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Throat swab -

A throat swab involves collecting a sample with a cotton swab to take culture from a patient’s throat and test for bacterial or viral infections that may be causing the cough.

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Blood tests -

Blood tests can determine if the body is fighting an infection, offering insights into a person’s potential immune responses or other systemic issues that could trigger a persistent cough.

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Chest imaging -

Chest X-rays or CT scans are often performed to evaluate the lung health of a patient, especially when it comes to individuals with a smoking history or preexisting medical conditions that affect respiratory function.

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Lung function tests -

Clinicians also sometimes conduct tests to measure the pattern of airflow in a person’s lungs. These usually involve spirometry tests, whereby a patient breathes in and out through a small plastic device.

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Acid reflux evaluation -

Acid reflux testing (including pH probes or upper endoscopy) assesses whether stomach acid irritates the esophagus and causes coughing. Endoscopy may also involve taking tissue samples for further analysis.

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The future of coughing -

Continued research is still being conducted as doctors and scientists attempt to determine how the human body works under such conditions. Only time will tell whether an answer (and a cure) becomes possible.

Sources: (National Geographic) (PBS) (WebMD) (Healthline)

See also: A guide to cough relief and over-the-counter medications

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