Coughing is a way for the body to remove foreign material from the upper respiratory system.
A dry cough is another name for a non productive cough, when the lungs are not producing sputum (phlegm), or producing very little sputum. A wet cough, also known as a productive cough, occurs when the lungs are producing more sputum, resulting in phlegm coming through the upper air passages. Many respiratory infections will begin with a dry cough and will turn into a wet cough as the infection develops. Other conditions, such as a chronic cough, may be continually dry. There is usually an audible difference between a dry and wet cough due to the lack or presence of sputum coming up.
As for which kind is more serious, a cough, whether dry or wet, can be a common symptom of any of many health complications. This can span from something so simple as postnasal drainage to a more serious illness of the lungs such as lung cancer or tuberculosis. In the case of whooping cough, when the infection causes a high production of sputum, infants risk asphyxiation from the high volume of phlegm they are unable to cough up.

There are some differences between a dry cough and a wet cough and those differences are mainly the mucous production or non mucous production with the cough. With a dry cough, there is a feeling of pricking or tickling in the throat. The cough associated with it is generally harsh sounding but it's a non productive type of cough. Usually a cough suppresant or cough drop of some sort will ease the symptoms.

A wet cough is associated with congestion in the trachea or lungs and will produce mucous, either clear in the case of allergies or yellow or greenish, associated with a viral infection or bacterial infection. In the case of a bacterial infection, antibiotics will be administrated by a doctor. Also some kind of cough medicine, an expectorant might be given to ease the congestion and allow the mucous to be expelled through coughing.

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