What Causes a Persistent Cough and Phlegm?

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Postnasal drip is the most common cause of chronic cough, according to WebMD. Postnasal drip occurs when the body produces more mucus than it needs and the excess mucus drains down the back of the throat. Common causes include allergies, sinus infection, pregnancy, deviated septum and changing weather, among others.

Treatment for chronic cough caused by postnasal drip depends on the cause. Doctors prescribe antibiotics if a bacterial infection causes the condition. Antihistamines used with steroidal nasal sprays can effectively treat allergy-induced postnasal drip, along with using dust mite proof covers on pillows and mattresses, washing bedding in hot water and using HEPA air filters. Thinning the mucus by taking guaifenesin, using nasal irrigation or running a humidifier may also alleviate symptoms, according to WebMD. People should contact a doctor if they also have a fever, wheezing, blood in the mucus or symptoms that last more than 10 days.

Other causes of chronic cough include asthma and gastroesophageal reflux disease, according to Mayo Clinic. If the cough is caused by asthma, people may experience symptoms when exposed to cold air or fragrances. A cough is the main symptom in cough-variant asthma. People with gastroesophageal reflux disease develop chronic cough due to irritation from stomach acid flowing into the esophagus.