A cough is a reaction to an airway irritation. It is generally the symptom of an illness or allergy. Some coughs are considered productive, which means they help to remove mucus from the lungs usually due to respiratory infections such as pneumonia and bronchitis. Others are considered nonproductive, and these are dry coughs that typically occur in response to exposure to an irritant such as smoke or because of a cold. Coughs may also be brought on by persistent problems including asthma, chronic obstructive pulmonary disease (COPD) or gastroesophageal reflux disease. The type of treatment for a cough will vary depending on its cause. Most coughs respond well to the use of a humidifier and increased fluid intake.