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Green sputum is often caused by a bacterial infection, though it also may appear several days in to a viral infection. If the sputum is this color from the beginning of symptoms, it is more likely to be the result of bacteria. It can be the result of a respiratory infection or post nasal drip from a sinus infection, although pneumonia, bronchitis, and sinusitis are all other common causes.
Sputum itself is typically made up of mucus secretions from the respiratory system, in addition to drainage from the sinuses. Many respiratory infections can result in the inflammation of the mucus membranes, which produce excess mucus. This excess is often expelled from the lungs through coughing, and can become mixed with post nasal drip to become sputum, which may be swallowed or spit out. A green color often indicates a bacterial infection within the respiratory system or the sinuses, though in some cases, the cause may be viral or environmental.
Bronchitis is an inflammation of the mucus membranes within the lungs, and may have viral, bacterial, or environmental causes. A small portion of the cases of acute bronchitis are caused by bacteria and will typically produce green phlegm. The chronic form, however, will often have environmental causes and can cause sufferers to cough up sputum for several months a year for years at a time. Root causes of chronic bronchitis and the phlegm it produces can be anything from cigarette smoke to excessive atmospheric pollution.
Another common cause of green sputum is sinusitis. This infection of the sinuses will typically result in some form of post nasal drip. A bacterial infection will usually cause green discharge, though viral sinusitis may also result in a similar coloration. Sinus infections can cause the nasal passageways to become clogged, allowing the mucus to become stagnant. Like bronchitis, sinusitis has both acute and chronic forms. Chronic sinusitis may have environmental or physiological causes, and internal problems with the nasal passages may be at fault.
Any infection or irritation to the upper or lower respiratory system can ultimately result in green sputum. In cases where the onset of illness are accompanied by clear sputum, taking nasal decongestants may help prevent it by promoting proper drainage. When a cough is producing green discharge, it is important for patients to avoid taking any medication that suppresses the cough. This may interfere with the natural ability of the body to discharge irritants, and may result in more severe illnesses, such as pneumonia.