Why do I keep coughing after catching a cold?

Coughing during illness helps protect the lungs from infection. But ongoing inflammation may irritate the nerve reflex that causes coughing.

Image source: Getty Images

Colds and other respiratory illnesses are never fun. After the sneezing, sniffles, and runny noses go away, one symptom usually remains: the cough. But why does a cough sometimes take so long to go away?

The main reason for a long-lasting cough is lingering inflammation, which can have many sources and is therefore difficult to treat.

These sources can include viral and bacterial infections that cause inflammation of the respiratory tract and nasal passages. This inflammation irritates the lining of the airways and nose and produces mucus — the phlegm and mucus associated with colds. Nasal inflammation can cause postnasal drip, which is mucus that drips from the nose down the throat and is a common cause of coughing.

When particles enter the airways through the nose or mouth, they trigger nerve receptors in the lungs that tell the brain - this is not what we want. Then, the pressure in the diaphragm increases and air is forced out, carrying away dust, food and mucus.

In addition to nasal inflammation, a cough may persist after a cold because airway inflammation may take several weeks to subside, and this time may be longer if someone has had a previous lung infection or smokes.

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When someone is sick, special immune cells called macrophages and neutrophils help fight respiratory infections. These cells are also inflammatory. Sometimes after a cold is over, these cells can stay in the airways and keep them inflamed, which is why a cough can continue after an infection.

At the same time, delicate airway tissues may be extra sensitive to particles that enter through the nose or mouth. That's because there's a complex system of nerves and muscles in the airways, throat, and brain that controls a cough. Just like you [use] a reflex hammer on your knee, your leg kicks out. There may be similar types of reflexes in the airways. In other words, the virus and mucus are the reflex hammer, and the cough is the kick. Once the inflammation subsides, this reflex becomes less sensitive and the cough goes away.

For a cough that lingers three to four weeks after becoming ill, there are home remedies and behaviors that can help shorten its duration (or at least relieve the symptoms).

If postnasal drip is accompanied by a cough, nasal saline or nasal steroids can help reduce the inflammation that causes the drip, and throat lozenges can also help calm the throat and suppress the cough.

According to a 2021 study published in the International Journal of Cardiopulmonary Medicine and Rehabilitation (opens in a new tab), research suggests that honey and saline solution can help relieve coughs. However, more research is needed to confirm the efficacy and safety of natural products.

While coughing can be annoying, it’s important to remember that coughing serves an immune function. If irritants and mucus remain in the airways, they can damage delicate airway tissue or the lungs, and even impede breathing. Exercising to stimulate deep breathing to loosen mucus, or taking expectorants that thin mucus and make it easier to cough up, can help remove those inflammatory irritants.

While it’s good to be considerate of others, sometimes it’s also important to let your cough flow.

While a lingering cough is most often caused by inflammatory irritation, people should see a doctor if a cough lasts for more than three to four weeks and is accompanied by other symptoms, such as fever, shortness of breath, or green and yellow mucus.

If a cough continues on its own for more than eight weeks, your doctor may need to do a chest X-ray or measure lung function to check for chronic obstructive pulmonary disease, lung cancer, emphysema, or other serious conditions.

Source: Chongqing Tianji Network Co., Ltd.

Source: Live Science "Why do coughs linger after a cold?"

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