Coughing is a normal reaction to irritants in your respiratory system. Coughing forcefully expels foreign bodies, mucus and other irritants, such as pollution, from your throat and clears them from your airway.

When a cough lasts longer than six to eight weeks, it's considered a chronic cough

Irritated Airways After a Cold or Flu

The most common cause of chronic cough is predictable. It's the aftermath of a cold or other viral infection. Most cold symptoms may go away after a few days. Your cough, though, can hang around for weeks because viruses can cause your airways to become swollen and oversensitive. This can last long after the virus is gone.

Postnasal drip

This is a sensation of mucus trickling from the back of your nose down into your throat. It may be due to hay fever, allergies or irritants. How postnasal drip causes a cough is still not clearly understood. In some cases, this sensation may not even be noticed. In chronic cough, postnasal drip may be due to inflammation of your nasal passages including your sinuses.

Gastroesophageal reflux disease (GERD)

With GERD, stomachacid, digestive enzymes andbile back up (reflux) into youresophagus. It may reach up to thevoice box. In severe cases, refluxmaterial may get into the lungs.These substances are irritating to your respiratory tract and can trigger a cough.Coughing itself may cause acid reflux, turning it into a vicious cycle. While heartburn is common in reflux, not everyone with reflux experiences it. Hoarseness, throat clearing, the sensation of a tickle in the throat and cough — usually when in an upright position — may be associated with GERD affecting the throat. This is called laryngopharyngeal reflux (LPR).

Pertussis

Chronic cough may be due to an unrecognized case of whooping cough (pertussis).

If your coughing is suspected of being caused by a bacterial infection, such as a persistent sinus infection or a lung infection, antibiotics may help.

Lung disorders

Chronic cough can be caused by airway damage called bronchiectasis, and by a condition that causes asthma-like symptoms, but with normal lung function (eosinophilic bronchitis).

Allergies and Asthma

Allergies and asthma are common causes of a cough. A cold can even cause an asthma attack. Some people learn they have asthma during a cold.