Most people are no longer infectious seven days after symptoms of a common viral infection begin. But a cough may persist for a few weeks, said doctors. (Photo: iStock/Liubomyr Vorona)

Is that three-week cough still contagious? What’s normal, why it lingers and what to look out for

Some people continue coughing after they recover from a common respiratory infection. Doctors explain why a cough can last for weeks, masking etiquette and red flags suggesting something more serious.

18 Jan 2026, 23:21 by Eveline Gan · CNA · Join

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That common respiratory virus you caught after the festive season seems to have finally run its course. The fever has broken and your energy levels have bounced back. You feel well enough to return to work or school and meet up with friends.

But there’s just one problem – that hacking cough that refuses to let up even weeks later and draws uneasy glances in the office or on public transport.

The sound of a persistent cough and clearing of throat often triggers discomfort in shared and enclosed spaces. For many, the worry is whether that lingering cough is contagious. And is masking up a good idea, especially while around vulnerable groups like young children, pregnant women and the elderly?

IS A LINGERING COUGH STILL CONTAGIOUS?

The cough may persist for up to four weeks, and in certain cases, can last as long as eight weeks, says one doctor. (Photo: iStock/PonyWang)

Although many people worry that a persistent cough weeks after a cold or the flu may still be infectious, experts say that this is usually not the case.

In most common viral infections, people are typically contagious for a few days before symptoms start and about three to seven days after symptom onset (the first appearance of symptoms), said Dr Mok Boon Rui, chief executive officer and founder of Pinnacle Family Clinic.

“Most individuals are no longer infectious seven days after symptom onset. However, the cough may persist for up to four weeks, and in certain cases, can last as long as eight weeks,” said Dr Joanne Khor, family physician and deputy head of Jurong Polyclinic, National University Polyclinics.

Dr Mok explained that even if the person feels “well” after the infection has cleared, the airways may not have fully recovered, causing a cough to linger.

“A lingering cough is usually caused by an increased airway sensitivity or irritation from postnasal drip after the infection,” added Dr Khor.

Postnasal drip occurs when mucus from the nose or sinuses drips down the back of the throat. This can irritate the throat and make one cough.

COUGH ETIQUETTE: SHOULD YOU MASK UP AT WORK?

After recovering from a cold or the flu, a lingering cough is usually not infectious, but it is a good idea to mask up when in shared spaces or when around vulnerable people. (Photo: iStock/Edwin Tan)

For those who feel well but continue to have a frequent or intense lingering cough, Dr Mok said that it is generally safe to return to work, exercise and social activities, provided there are no red flags symptoms.

At this stage, self-isolation, avoiding work or school solely because of a lingering cough, and requesting for antibiotics for a dry or improving cough are usually not necessary, said Dr Mok. Repeated COVID-19 or flu testing is also not needed, when symptoms seem stable or are improving, he added.

“If someone has a lingering cough but otherwise feels well, the risk of infection to others, including vulnerable groups, is usually low. That said, simple, targeted precautions are sensible and effective, especially around elderly parents, young children, pregnant women, or immunocompromised individuals,” said Dr Mok.

These include practising good cough etiquette by coughing into a tissue or your elbow, maintaining good hand hygiene, and improving ventilation around shared spaces, and wearing a mask.

Dr Khor pointed out that wearing a mask is considered good cough etiquette, even after a person is no longer infectious.

“Coughing releases more particles than simply breathing or talking. Although you might not be infectious, coughing can still spread droplets by releasing airway secretions into the air. A mask helps lower this risk,” she said. “Additionally, wearing a mask warms and moistens the air you inhale, which may help make your cough less severe.”

WHO IS MORE LIKELY TO GET A PERSISTENT COUGH

Post-infection coughs are usually due to greater airway sensitivity or throat irritation from postnasal drip. (Photo: iStock/winsterphoto)

Certain underlying conditions can make the airways more sensitive, increasing the risk of a lingering post-infectious cough. These include asthma, allergic rhinitis or gastro-oesophageal reflux disease (GERD).

In asthma, the airways in the lungs are extra sensitive and easily irritated, said Dr Khor. “After a respiratory infection, this sensitivity may remain for some time, so even small irritations, like cold air, dust or exercise, can trigger coughing,” she explained.

Allergic rhinitis contributes to increased mucus production and swelling in the nasal passages, which can lead to a postnasal drip. In GERD, stomach acid travels upwards into the oesophagus and may reach the throat. This acid irritation can activate the nerves in the throat that trigger the cough reflex.

“When the throat becomes irritated (from postnasal drip or reflux), it signals the body to cough as a protective response,” Dr Khor said.

Smokers are also more likely to develop a lingering cough after an infection. “Smoking increases inflammation in the airways and damages the tiny hair-like structures in the lungs (called cilia) that help clear mucus,” she added.

THE RED FLAGS: WHEN TO SEEK MEDICAL ATTENTION

You might want to see a doctor promptly if there is shortness of breath, chest pain, haemoptysis (coughing up blood), weight loss, night sweats, or if the cough improves then worsens. (Photo: iStock/PonyWang)

According to European Respiratory Society guidelines, a chronic cough is generally defined as a cough lasting more than eight weeks and more than four weeks in children, said Dr Khor. However, she noted that the patient’s medical history, specific risk factors and other symptoms is also considered when determining if a cough is of a prolonged nature.

“Your doctor may ask you about factors that trigger your cough and when it is most severe in the day. You may also be asked about your past medical history and if you are taking any long-term medications, as some medicines can have coughing as a side effect,” Dr Khor said.

Certain symptoms may warrant further diagnostic tests and investigations. Dr Khor advised seeing a doctor promptly if there is shortness of breath, noisy breathing, chest pain, haemoptysis (coughing up blood), weight loss, night sweats, or if the cough improves then worsens.

“People with pre-existing lung conditions like asthma, chronic obstructive pulmonary disease (COPD), or bronchiectasis (a chronic lung condition where the airways become wider and damaged) should also consult their doctor promptly if they feel unwell,” she said.

Dr Mok added that paroxysmal coughing fits can be another red flag, especially if they are accompanied by other symptoms. These are sudden, violent and uncontrollable coughing episodes. When paired with post-tussive vomiting (vomiting after severe coughing) and a “whoop” sound, they may suggest pertussis, or whooping cough, which is a highly contagious bacterial infection of the respiratory tract.

WAYS TO CALM A STUBBORN COUGH

Staying hydrated maintains throat moisture, reducing irritating and cough triggers. Taking small sips of water can also help suppress cough, said an expert. (Photo: iStock/Suriyawut Suriya)

There some simple practical ways that help soothe throat irritation and ease a lingering cough. One way is to stay hydrated throughout the day.

“Adequate hydration maintains throat moisture, thereby reducing sensitivity to irritation and potential cough triggers. Taking small sips of water when experiencing the urge to cough can also serve as an effective strategy for suppressing coughs,” said Dr Khor.

Keeping a sugar-free sweet in the mouth can be helpful when coughing would be inconvenient, for example, during an important meeting or on a crowded train, as you cannot cough while swallowing, she added.

Other measures include avoiding smoking, and reducing exposure to household irritants such as dust, fumes and strong cleaning agents as these can perpetuate cough hypersensitivity, said Dr Khor.

According to Dr Mok, a common myth is that strong cough syrups are the best solution for calming a cough, when many provide minimal benefits. Hydration, honey and avoiding triggers often work just as well, he said.

Dr Khor added: “Although cough syrups may provide symptomatic relief, they can cause sedation which is especially concerning for older adults due to the increased risk of falls.”

Dr Mok also cautioned against assuming that “natural” cough remedies are always safe or effective. “Some herbal remedies may interact with medications, or are unsuitable during pregnancy or for children,” he said.

As for steam inhalation, there is limited evidence regarding its effectiveness. “It may be considered due to its minimal side effects, provided appropriate precautions are taken to avoid burns,” said Dr Khor.

The doctors emphasised the importance of seeing a doctor, especially if the cough worsens or there are red flags highlighted previously. “It is important to first identify and manage any possible underlying causes of the cough. For example, chronic lung conditions such as asthma and COPD might need to be treated with inhalers,” said Dr Khor.

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